fheroes2 is a recreation of Heroes of Might and Magic II game engine
Solar2D Game Engine main repository (ex Corona SDK)
Open 3D Engine (O3DE) is an Apache 2.0-licensed multi-platform 3D
Animation Compression Library
Opensource crossplatform Fallout 2 game engine writen in C++ and SDL
RTSish Game Engine
Free and Open Game Programming Language for Windows and GNU/Linux
Game engine for playing tomb raider 1 - 5 levels.
Community-driven game engine
Multi-platform game engine similar to old Megaman with a stage editor
Paintown is a 2d fighting game engine.
Mahasona engine is an open source game engine.
Open Source 3D Game Engine
a flexible game engine
3D game engine for C and C++
Tactical, turn-based game engine, that uses OpenGL and WinAPI
A very small multi-platform game engine for creating desktop games.
WGFX 2D Game Engine
A cross platform 3d c++ game engine