It is a program (virtual machine) that plays some of the older adventure/roleplaying games. There is also the possibility to use Dosbox, with the difference being that DOSBox runs the game how you used to run it in DOS, while SCUMM runs it through its own executable which also works on multiple platforms. This makes it much easier to for example install something like Lucas Arts games - basically just plug and play and no need to run different commands or try to figure out the best sound/picture/speed, etc. They also have some cool addons for games, like subtitles for Blade Runner. They don't support a lot of games, but those they do support work pretty well. I have had good experiences using it for playing games like DOTT, Simon the Sorcerer, Gabriel Knight, Indiana Jones and the Fate of Atlantis, Sam & Max, Full Throttle, and BASS.