Ren'Py

Ren'py is most often used for visual novels and therefore thought of as a specialized and simple game engine not suitable for anything else. But it is quite capable of any type of game. There are some complex RPGs, Simulation, Action, and Strategy games made using it. It will even do Wolfenstein 3D type (ray casting) graphics. But possibly the most impressive use of Ren'py is IIOS, a full desktop environment with multitasking, windows, picture viewer, movie player, IRC client, minesweeper and other games, web browser, and media player that is partially WinAmp compatible.