a free / freeware open source tool for 2-D game development. It is designed for the Windows 9x/DirectX platform, and targeted at people spanning a range of skill levels.
With hundreds of published titles, 3D GameStudio authoring suite for 2D, 3D realtime applications. It combines the C-Script programming language with a high-end 3D engine, a 2D engine, a physics engine, a level, terrain and model editor, etc...