by DOSBox Crew
Probably the best and most important tool if you want to play the Dos classics from the good old past on nowadays computers.
Here's what the developer wrote about it:
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. (taken from the official homepage)