DOSBox is a DOS-emulator that uses the SDL-library. This makes DOSBox very easy to port to different platforms. DOSBox has already successfully been ported to BeOS, Linux, MacOS X, as well as Windows.
DOSBox also emulates CPU:286/386 realmode/protected mode, Directory FileSystem/XMS/EMS, Tandy/Hercules/CGA/EGA/VGA/VESA graphics, and SoundBlaster/Gravis Ultra Sound card for excellent sound compatibility with older games.
DOSBox is a great DOS-emulator and can run all sorts of classic titles from a bygone gaming era. The learning curve is quite steep, and if you are a beginner then you may find it a tad difficult to get to grips with. Apart from that, it is a great way to run plenty of classic games that don't run on a new computer!