ScummVM is a program which allows you to run certain classic graphical point-and-click adventure games, provided you already have their data files. The clever part about this: ScummVM just replaces the executables shipped with the games, allowing you to play them on systems for which they were never designed!
ScummVM supports many adventure games, including LucasArts SCUMM games (such as Monkey Island 1-3, Day of the Tentacle, Sam & Max, ...), many of Sierra's AGI and SCI games (such as King's Quest 1-6, Space Quest 1-5, ...), Discworld 1 and 2, Simon the Sorcerer 1 and 2, Beneath A Steel Sky, Lure of the Temptress, Broken Sword 1 and 2, Flight of the Amazon Queen, Gobliiins 1-3, The Legend of Kyrandia 1-3, many of Humongous Entertainment's children's SCUMM games (including Freddi Fish and Putt Putt games) and many more.
You can find a full list with details on which games are supported and how well on the compatibility page. ScummVM is continually improving, so check back often. Among the systems on which you can play those games are Windows, Linux, Mac OS X, Dreamcast, PocketPC, PalmOS, AmigaOS, BeOS, OS/2, PSP, PS2, SymbianOS and many more...
Our forum and IRC channel, #scummvm on irc.freenode.net, are open for comments and suggestions. Please read our FAQ before posting.