The 1989 classic, Prince of Persia by Brøderbund is now free.
The classic, MS-DOS version of Prince of Persia from 1989 is now a free open source port that is capable of running natively on PC and Linux.
The classic Prince of Persia was great, even before Ubisoft got rights to the catalog. The levels were dark and limited with colours, but the gameplay was fantastic. Deadly traps, sword battles, and deadly environments were all part of what made the title great.
You can download the game for free here