Commercial games that became freeware
Here is a Wikipedia list of commercial games that turned to freeware. (Some may only be downloaded from certain websites and with the explicit permission of the copyright owner.)
There is also a list with games that were originally released as freeware and another one for open source and commercial games re-released as open source.
The x-commercial now-freeware games include Akalabeth, Command & Conquer, Wolfenstein, Grand Theft Auto…
Click on the title of a game to learn about it and get download links.