Alternatives to VCMI

Real-time strategy game engine for Westwood games

2D and 3D game engine

C# scripting capable version of Godot game engine

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

First person shooter engine

Engine for iD software's Quake

Open-source continuation of Bungie's Marathon 2 game engine

Build engine port backed by GZDoom tech

Enhanced source port of Doom, Heretic, and Hexen

Lua-based game engine

Complete development tool for making 2D games

Voxel game-creation platform