KorGE Game Engine. Multiplatform Kotlin Game Engine & Korlibs
GemRB is a portable open-source implementation of the Infinity Engine
Game engine supporting many 3D/2D formats and graphic effects
Cross-platform 2D game engine (+ full OpenGL, +full OpenGL ES )
An isometric arcade-style game of skill, puzzles and exploration
Orx: Data-Driven Game Engine
RTSish Game Engine
DOOM / Heretic / Hexen source port with enhanced graphics and UI
Low-Level Game Engine for Retro Platforms
Multi-platform game engine similar to old Megaman with a stage editor
Paintown is a 2d fighting game engine.
A generic 2D engine for any kind of game
Game engine supporting many 3D/2D formats and graphic effects