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...
a game programming library for C/C++ developers distributed freely, supporting the following platforms: DOS, Unix (Linux, FreeBSD, Irix, Solaris, Darwin), Windows, QNX, BeOS and MacOS X. It provides many functions for graphics, sounds, player input, etc..
Hardware accelerated 2D full featured middleware for all who want to develop commercial quality 2D games rapidly and easily. It covers all imaginable 2D game genres (DirectX)
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.