For anyone who cares about legality, do not touch Internet Archive (archive.org) with a 10 foot pole. That place is one of the biggest collections of warez known to man today.

Just note that abandonware is not a legal term, and the ScummVM team consider it piracy/warez. You don't get supported with problems by ScummVM if you play an illegitimately acquired copy of a game.

There ARE some games which are released by the original developers for free. Beneath a Steel Sky can even be found in the Debian and Arch repositories, for example.