Descent 3 by Outrage Entertainment
GemRB is a portable open-source implementation of the Infinity Engine
Game engine supporting many 3D/2D formats and graphic effects
A Tile-based Game Engine written in C# mimicing retro consoles.
Low-Level Game Engine for Retro Platforms
Portable game engine with main focus on point-and-click adventures
Flexible and easy-to-use 2d game engine
Multi-platform game engine similar to old Megaman with a stage editor
An advanced flexible game engine for Java.
An online multiplayer turn based strategy game and board game engine.
A generic 2D engine for any kind of game
A 3D, fully concurrent game engine
A multiplatform game engine for interactive fiction experiences
Role Playing Game Engine