DOSBox is a DOS-emulator that uses the SDL-library which makes DOSBox very easy to port to different platforms. DOSBox has already been ported to many different platforms, such as Windows, BeOS, Linux, MacOS X...
DOSBox also emulates CPU: 286/386 realmode/protected mode, Directory FileSystem/XMS/EMS, Tandy/Hercules/CGA/EGA/VGA/VESA graphics, a SoundBlaster/Gravis Ultra Sound card for excellent sound compatibility with older games...
You can "re-live" the good old days with the help of DOSBox, it can run plenty of the old classics that don't run on your new computer!
DOSBox is totally free of charge and OpenSource.
DOSBox emulates an Intel x86 PC, complete with sound, graphics, mouse, joystick, modem, etc., necessary for running many old MS-DOS games that simply cannot be run on modern PCs and operating systems, such as Microsoft Windows XP, Windows Vista, Linux and FreeBSD. This environment is complete enough to run many classic MS-DOS games completely unmodified. However, it is not restricted to running only games. In theory, any MS-DOS or PC-DOS (referred to commonly as "DOS") application should run in DOSBox, but the emphasis has been on getting DOS games to run smoothly, which means that communication, networking and printer support are still in early development.
DOSBox also comes with its own DOS-like command prompt. It is still quite rudimentary and lacks many of the features found in MS-DOS, but it is sufficient for installing and running most DOS games.