They are free, they are legal, some of them are really worth playing.
List of commercial games released as freeware:
http://en.wikipedia.org/wiki/List_of...ed_as_freeware
List of freeware games:
http://en.wikipedia.org/wiki/List_of_freeware_games
List of Open Source games:
http://en.wikipedia.org/wiki/List_of_open_source_games
List of free first-person shooters
http://en.wikipedia.org/wiki/List_of...erson_shooters
I would recommend the surprisingly awesome Sauerbraten aka Cube 2
Abandonia Reloaded:
http://www.reloaded.org/
Remain in play:
http://www.remaininplay.com/
And finally the place to make DOS games run under XP:
http://vogons.zetafleet.com/index.php
Enjoy !
