Alternatives to Aleph One

2D and 3D game engine

Real-time strategy game engine for Westwood games

C# scripting capable version of Godot game engine

Open-source, cross-platform game engine designed to be used by everyone

First person shooter engine

Open-source engine for Heroes of Might & Magic III

Build engine port backed by GZDoom tech

Engine for iD software's Quake

Enhanced source port of Doom, Heretic, and Hexen

Complete development tool for making 2D games

Game engine for development of desktop, mobile and web games

Lua-based game engine