2D Game Engine
mGSTEP port of the Cube game engine
KlayGE is a cross-platform open source game engine
A cross-platform 2D game engine
A cross platform Lua based game engine
A fast, scalable, distributed game server engine/framework for C++
Cross-platform 2D and 3D game engine
Opensource Game Studio
IGS Labs
Free and Open Game Programming Language for Windows and GNU/Linux
Low-Level Game Engine for Retro Platforms
Blueshift is a cross-platform 3D game engine implemented in C++
Real-time RPG for PC/tablet/phone; multiple quests and random dungeons
Portable game engine with main focus on point-and-click adventures
Game engine for playing tomb raider 1 - 5 levels.
scriptable game engine with built-in support for 2D graphics and sound
Intrinsic is a Vulkan based cross-platform game and rendering engine
C++11 cross-platform game engine using SDL2
Multi-platform game engine similar to old Megaman with a stage editor