The game+engine source code is integrated into ScummVM, which is FLOSS. The
game data (images, maps, texts, fonts, voice, music, etc.) is not important
to be free, since it does not consist of any code, and thus it cannot do any
harm (+ theoretically, it can be easily inspected/modified). Many game source
code was donated by the game developers themselves, so it is a good thing to
support them by buying these games. Just check out eBay, where you can find
them cheap.
You can find the list of supported games here. My favourite one is
Toonstruck, which I bought before I was enlightened by Richard Stallman, and
the free software movement. Also check out other games like Maniac Mansion
(the first game built in the SCUMM engine), the King's Quest series, Gold
Rush! (awesome game!), Leisure Suit Larry, and many many others. Although the
graphics are very oldie, they are still considered to be the best.
Also, don't forget to check out the ScummVM Music Enhancement Project by
James Woodcock, for improved music quality.
