With four bonus downloads.
GOG.com are offering Worms Forts: Under Siege for free until 11:00 AM PST on December 17, 2015. That game normally sells for $5.99.
Worms Forts: Under Siege is a strategy game that was released on November 19, 2004. The GOG.com version is confirmed to be compatible with Windows XP, Vista, 7, 8 and 10.
The GOG.com version of that game also includes the following bonus downloads:
Image credit: GOG.com