Two engines. Three decades. Dozens of games. And somehow, in 2026, both are producing work that rivals anything built on Unreal Engine 5 or Unity. The GZDoom source port — a community fork of id Software’s original Doom engine, whose foundational code was written when Bill Clinton was in his first term — and Ken Silverman’s Build Engine, the 2.5D powerhouse behind Duke Nukem 3D, Blood and Shadow Warrior, should by all rights be museum pieces. Instead, a generation of indie developers has adopted them as creative constraints, squeezing performance, interactivity and visual fidelity out of technology that predates most of their players. The result is a renaissance of fast, tactile, deliberately retro first-person shooters — a subgenre colloquially known as boomer shooters — that treat old engines not as limitations to apologize for, but as instruments to master.
The engines that refuse to die
GZDoom began as a fork of ZDoom, itself a source port made possible by John Carmack’s 1997 release of the Doom source code. What started as a project to add OpenGL rendering to a 30-year-old engine has evolved into something barely recognizable from its origins. The current GZDoom supports Vulkan rendering, physically based rendering materials since version 4.5, dynamic lighting with real-time shadows, post-processing effects including SSAO and bloom, 3D model support, high-resolution textures up to 8K, and a modern object-oriented scripting language called ZScript that gives developers access to engine internals with a power comparable to C#. gzdoom.cc +1
The Build Engine, meanwhile, has survived through EDuke32 — a fork maintained primarily by the Voidpoint development team, the same group responsible for Ion Fury. EDuke32 modernized the Build Engine with support for contemporary operating systems, expanded scripting capabilities, and advanced rendering features while preserving the engine’s signature sector-based geometry and sprite-driven world representation. A more recent project called Raze, backed by GZDoom technology, has further expanded Build Engine preservation by providing a unified source port capable of running Duke Nukem 3D, Blood, Shadow Warrior and Powerslave from a single executable.
Selaco: GZDoom’s technical showpiece
When Selaco entered Early Access on May 31, 2024, it immediately became the most ambitious GZDoom project ever released commercially. Developed by Altered Orbit Studios, the game is a sci-fi shooter set in an underground colony on Mars, following security officer Dawn Collins as she unravels a violent invasion. What sets Selaco GZDoom apart from other GZDoom projects is the sheer scale of its technical achievements — features that most developers would assume require a modern engine. [web_15_0_20][web_15_0_22]
Digital Foundry’s technical review highlighted the game’s dynamic lighting system, which includes muzzle flash shadows and colored light sources reminiscent of late-90s Unreal. Every bullet interacts with surfaces correctly, and the environment destruction system uses voxel-based objects that can be progressively damaged and destroyed — chairs scatter, screens shatter, fire extinguishers release powder that interacts with nearby light sources. The enemy AI varies aggression and intensity, with foes that flank, use cover, retreat from grenades and pursue the player through complex level geometry. None of this is typical GZDoom territory. [web_15_0_22]
The game shipped its first chapter with 31 maps ranging from five to thirty minutes each, 11 weapons with upgrade kits, 14 enemy types, full voice acting, cutscenes and a dedicated soundtrack. A Steam Workshop integration opened the doors to community mods from day one. As of early 2026, Selaco holds an 89% positive rating across approximately 5,000 Steam reviews. [web_15_0_0]
Chapter 2, announced in December 2025 and planned for release in 2026, promises even more dramatic improvements. Altered Orbit Studios revealed a new baked-lighting system that adds detailed shadows to nearly every surface while simultaneously improving performance — areas that previously had many dynamic lights now render more efficiently. Navigation, a common player complaint in Chapter 1, will be addressed with a goal indicator on the map screen. An Incursion Mode, inspired by Rainbow Six’s Terrorist Hunt and Gears of War’s Horde Mode, is being developed as a separate combat campaign. The AI is receiving a substantial overhaul, with enemies gaining improved pathfinding and better cover utilization. [web_15_0_2][web_15_0_4]
The Build Engine legacy: from Duke Nukem 3D to Ion Fury
Ken Silverman’s Build Engine powered the most iconic first-person shooters of the mid-1990s. Its sector-based 2.5D architecture — which used two-dimensional map geometry extruded into pseudo-3D — was technically inferior to id Software’s true-3D Quake engine, but it offered something Quake could not match: extraordinary environmental interactivity. Build Engine retro games featured destructible walls, functional toilets, interactive light switches, mirrors, driveable vehicles and room-over-room architecture that gave levels a sense of place that competitors lacked. gamefaqs.gamespot.com +1
Duke Nukem 3D (1996), Blood (1997) and Shadow Warrior (1997) formed the “big three” of Build Engine releases, but the engine also powered lesser-known titles like Redneck Rampage, Powerslave, NAM, WWII GI and the infamous Extreme Paintbrawl. After WWII GI in 1999, no commercial game used the Build Engine for two decades — until Voidpoint and 3D Realms released Ion Fury in 2019, built on EDuke32. Ion Fury was the first original commercial Build Engine game in twenty years, and it proved that the engine still had untapped potential. Its sprawling, meticulously crafted cyberpunk levels, dense environmental detail and tight gunplay earned it a place among the best boomer shooters ever made. moddb.com +1
Ion Fury expansion: Aftershock pushes the engine further
The Ion Fury expansion, titled Aftershock, was released for PC in October 2023 and arrived on PlayStation 4, Xbox One and Nintendo Switch on October 16, 2025. The expansion picks up moments after the base game’s conclusion, with Shelly “Bombshell” Harrison pursuing the escaped Dr. Heskel through brand-new zones. What makes Aftershock remarkable is not just its content — 15 new levels, new enemy types, a new weapon called the Cluster Shot launcher, an Angel of Death difficulty level and an Arrange Mode that remixes all 28 original campaign levels — but the technical feats it achieves within the Build Engine’s constraints. [web_15_0_6][web_15_0_5]
Voidpoint implemented high-speed vehicle combat using a driveable “rotorcycle” across multiple levels, a sequence that recalls Half-Life 2’s Water Hazard chapter. The expansion features speeding trains, thrashing machinery and collapsing buildings — effects previously thought impossible within the Build Engine’s sector-based architecture. Arrange Mode goes beyond simple enemy rearrangement, actually modifying level geometry in some cases to create a fresh experience for returning players. The console versions were specifically optimized, with the Nintendo Switch port running at 720p/60fps in handheld mode and 1080p/60fps docked. [web_15_0_7]
Comparing the two engine ecosystems
Understanding why developers choose these aging engines requires looking at what each one offers — and what each one cannot do. The following comparison outlines the technical capabilities and limitations that shape every game built on these foundations.
| Feature | GZDoom | Build Engine (EDuke32) |
|---|---|---|
| Rendering API | OpenGL 3.3+, Vulkan 1.1+ | Software renderer, OpenGL (EDuke32) |
| Geometry | Sector-based with 3D floors and slopes | Sector-based 2.5D with room-over-room |
| Lighting | Dynamic lights, shadowmaps, spotlights, PBR | Static lighting, limited dynamic effects |
| Scripting | ZScript (object-oriented), ACS | CON scripting, Lua (EDuke32 extensions) |
| Model support | MD3, OBJ, 3D models | Sprite and voxel-based only |
| Post-processing | SSAO, bloom, depth of field, custom shaders | Minimal post-processing support |
| Texture resolution | Up to 8K supported | Limited by engine architecture |
| Physics | Box2D-based collision, trigger physics | Sector-based collision, limited physics |
| Notable commercial game | Selaco (2024) | Ion Fury (2019), Aftershock (2023) |
| Source availability | Open source (GPL) | Open source (EDuke32) |
| Multiplayer | Native co-op and PvP | Native co-op and PvP |
The comparison reveals that GZDoom has pulled significantly ahead in rendering capability, while the Build Engine retains a unique identity through its environmental interactivity and sprite-based aesthetic. Developers choose between them not based on raw power, but on the kind of game they want to make — GZDoom for modern-feeling shooters with complex lighting and 3D elements, Build Engine for authentic 90s-level design with dense interactivity.
Blood 1997 source port: the ongoing preservation battle
Among all Build Engine games, Blood holds a unique status. Developed by Monolith Productions and released in 1997, it is widely considered the best of the Build Engine titles — a horror-themed shooter with exceptional level design, memorable weapons and a dark, atmospheric tone that set it apart from the tongue-in-cheek Duke Nukem 3D and Shadow Warrior. Yet Blood’s source code was never officially released, making it the only major Build Engine game without a sanctioned source port. Monolith was acquired by Warner Bros., which owns the Blood trademark and intellectual property, creating a licensing situation that has stymied official preservation efforts. [web_15_0_15]
The community has worked around this limitation through multiple projects. NBlood, released in January 2019 by developer Alexey Khokholov (Nuke.YKT), is a reverse-engineered source port built on EDuke32 that runs Blood’s original map and data files without requiring the proprietary source code. BloodGDX, created by developer Alexander “DrakDom” Makarov, offers another approach using Java. The Raze engine, which uses GZDoom’s rendering technology, also supports Blood alongside other Build Engine games. These projects have made Blood playable on modern systems with enhanced features like widescreen support, improved performance and quality-of-life improvements. [web_15_0_15]
Officially, Nightdive Studios released Blood: Fresh Supply in May 2019, a remaster built on their proprietary Kex Engine that added 4K resolution support, ambient occlusion, anti-aliasing and other modern features. In December 2025, Nightdive and Warner Bros. released Blood: Refreshed Supply for PC, PlayStation 4, PlayStation 5, Xbox One, Xbox Series X/S and Nintendo Switch — a version built from the ground up using the original source code, making it the most accurate official release to date. A Nintendo Switch 2 port followed on May 7, 2026. Refreshed Supply includes the community mods Marrow and Death Wish, completely redone cutscenes, weather effects, an archival vault with concept art and cut levels, and tweaked enemy behaviors. [web_15_0_15][web_15_0_16]
The modern boomer shooter landscape
The revival of retro engines has spawned a subgenre that now has its own Steam tag and a dedicated community. Modern boomer shooters share a set of design principles that distinguish them from mainstream AAA shooters — and the range of engines powering them has expanded well beyond GZDoom and Build.
The following titles represent the diversity of the modern boomer shooter scene:
- DUSK (2018) — Built on a custom engine by David Szymanski, this Quake-inspired shooter is widely credited with launching the boomer shooter revival. Its combination of fast movement, resource management and atmospheric level design set the template that many subsequent games followed. [web_15_0_11]
- Ion Fury (2019) — The first commercial Build Engine game in twenty years, proving that the engine still had untapped creative potential. Its sequel, Phantom Fury (2024), moved to Unreal Engine but maintained the retro aesthetic.
- Selaco (2024) — The most technically ambitious GZDoom game ever made, blending F.E.A.R.-style combat with Doom-engine destructibility and professional production values including voice acting and cutscenes. [web_15_0_20]
- CULTIC (2022) — A Blood-inspired shooter by Jasozz Games, built on a custom engine but channeling the Build Engine’s horror atmosphere and shotgun-heavy combat. [web_15_0_11]
- Prodeus (2022) — A Doom-inspired shooter that uses modern rendering technology to create a “demake” aesthetic, blending 3D models with sprite-based enemies. [web_15_0_11]
- Warhammer 40,000: Boltgun (2023) — A licensed Warhammer shooter that embraces the boomer shooter formula with pixel-art visuals and arena-style combat encounters. [web_15_0_13]
- Turbo Overkill (2024) — A hyper-fast shooter where the protagonist has a chainsaw leg, blending boomer shooter pace with over-the-top action. [web_15_0_12]
- Gravelord (2026) — A dark fantasy boomer shooter released in Early Access in January 2025, with a full launch in May 2026, featuring hand-crafted levels and a tarot card power system.
The diversity of this list reflects a subgenre that has grown far beyond its origins. Some games use the actual engines that inspired the genre — GZDoom and Build — while others build custom engines that replicate the aesthetic and feel. The common thread is a design philosophy: fast movement, no health regeneration, multiple weapons carried simultaneously, secret-filled levels and enemies that force the player to keep moving rather than hiding behind cover.
Why old engines still matter in 2026
The question of why developers continue to use engines that are decades old has a more nuanced answer than simple nostalgia. These engines impose creative constraints that can produce results difficult to achieve with modern technology. The sector-based geometry of the Build Engine forces level designers to think in terms of connected spaces and sightlines, producing maps with a density and intentionality that open-world engines rarely match. GZDoom’s scripting system, while technically limited compared to Unity or Unreal, is accessible enough that a single developer can build an entire game without a team of programmers — Selaco was created by a small indie studio, not a AAA company. [web_15_0_22]
Performance is another factor. GZDoom runs on virtually any hardware made in the last decade, from low-end laptops to high-end gaming PCs. The Build Engine, even in its EDuke32 form, has minimal system requirements. This accessibility matters for both developers and players — an indie team can target a wider audience, and players with older hardware can participate in a genre that AAA development has largely abandoned. The financial model is also different: boomer shooters typically launch at $20–30, a fraction of the $70 price point of AAA releases, making them accessible to a broader audience.
The creative constraints of old engines also produce distinctive aesthetics. The voxel objects in Selaco, the sprite-based enemies in Ion Fury, the sector-based geometry that gives Build Engine maps their characteristic look — these are not limitations being apologized for. They are design choices that give each game a visual identity that stands apart from the homogeneous realism of modern engines. In a market saturated with Unreal Engine 5 titles that share the same lighting model and material system, games built on GZDoom and Build look like nothing else.
The road ahead for retro FPS
As 2026 unfolds, the boomer shooter scene shows no signs of slowing down. Selaco’s Chapter 2 is in full production, with Altered Orbit Studios describing it as feeling like “a sequel on its own.” A third chapter will follow, completing the Early Access roadmap. The Ion Fury franchise continues with Aftershock now available across all major platforms, and while Phantom Fury moved to Unreal Engine, the Build Engine lineage remains alive through community projects and the ongoing EDuke32 development. Blood: Refreshed Supply brought the most accurate official version of the 1997 classic to modern consoles, including the Switch 2, closing a preservation gap that had persisted for nearly three decades.
The broader retro FPS pipeline for 2026 includes titles like Gravelord, Project Warlock: Lost Chapters, Age of Hell, RetroSpace and ExeKiller — each bringing its own engine choice and design philosophy to a genre that has proven remarkably resilient. What began as a niche revival fueled by a handful of passionate developers has become a sustainable corner of the games industry, one where old engines and new ideas coexist productively. The technology may be vintage, but the ambition driving it is thoroughly contemporary — and the results speak for themselves.