The flexible game engine
Free game engine for development of desktop, mobile, and web games
Stride (formerly Xenko), a free and open-source cross-platform C# game
3D Game engine with editor
Cross-platform, open source, and super fast MUD client with scripting
Descent 3 by Outrage Entertainment
High performance UI layout library in C
A game framework written with osu! in mind.
Games for tomorrow's programmers
Delphi Java - VRCalc++ OOSL (Script) and + (Binary Exec Distro)
Action RPG that's easy to mod
Combat Flight Simulator for LINUX. WW2. Network and VOIP. Open-source.
A cross-platform port of Hexen II game.
A free 3d game for PC that does not limit the player. Fight,Build,Gain
LDraw™ editor for LEGO® style digital building instructions.
A promising chess program
Galgame's Multilingual Real-time Machine Translation Tool
A cross-platform, open-source, pure C game engine for mobile game
An elegant Go board and SGF editor for a more civilized age
3D C++ Game Engine - yet another open source game engine
Modern 3D engine and IDE written using C# and C++.
A mapping tool for text-based games like text adventures, MUDs, etc.
Solve Go problems (based on GoGrinder GoGrinder.sf.net )
Children's learning programming language Karel the Robot in 3D