GemRB is a portable open-source implementation of the Infinity Engine
Game engine supporting many 3D/2D formats and graphic effects
Zoomable user interface (ZUI) with file manager, file viewers and more
Arianne is an engine to develop multiplayer online games like Stendhal
Orx: Portable Game Engine
portable o2em launcher
jfCraft : Yet Another Minecraft Clone
Low-Level Game Engine for Retro Platforms
Portable game engine with main focus on point-and-click adventures
SJCE - free portable cross-platform graphical chess game, 100% Java.
scriptable game engine with built-in support for 2D graphics and sound
distraction-less card game
Sims 3 (and other) game package library
Multi-platform game engine similar to old Megaman with a stage editor
a very lightweight advanced terrain-rendering and 3D map rendering sys
API for all possible cellular automata that work same at all angles
plugin-based RPG manager in C++ and Qt5
Portable Pokémon Mini Emulator
This is a hacking style game set in the early '80s
A traditional top-down OpenGL car racing game