Crocotile 3D
Use 2d tiles to create 3d models!
Easy FPS Editor CE v1.10.5
A free tool for creating oldschool FPS games
SpriteMancer
The all-in-one tool to create and animate effects
Easy FPS Editor v1.6 (Unsupported, read description)
Simple way to create an old-school First Person Shooter!
Easy FPS Editor 1.5 - PRO (OUTDATED, CHECK DESCRIPTION)
Simple way to create an old-school First Person Shooter! PRO version
Castle Game Engine
Cross-platform (desktop, mobile, console) 3D and 2D game engine. Visual editor. glTF, X3D, Spine. Modern Pascal code.
Game Asset Crafter
Assemble model primitives like bricks and blocks
Simulation Starter Kit (Engine, Editor and SDK)
A plugin-based 3D engine, editor and SDK (C++ / CMake / OpenGL / GLSL / SDL2 / Lua)
PapaiArt Tools - Level Editor
Doom-style Level Editor
Godot Online Shader Editor
...edit your shader online taking many examples as a base