DOSBox
DOSBox is an emulator which creates a DOS-like environment intended for running MS-DOS-based PC computer games which may not run properly on newer PCs and may not run at all on non-IBM PC compatibles (e.g. Macintosh). It also allows such games to be run on other operating systems that do not normally support DOS programs. DOSBox is open source and available for many operating systems, such as Linux, FreeBSD, Windows, Mac OS X, OS/2 and BeOS. Recently, it has even been ported to the GP2X [1] device.
