OMG I used to love this game!
Consists of Jill of the Jungle, Jill Goes Underground and Jill Saves the Prince, and they're all included in the package. GOG hasn't set an end date for the freebie deal, so presumably it'll stay free forever?
The cult classic sees you control Jill as she swings, jumps and kicks her way through the jungle-themed levels. If you find magical icons, then Jill will transform into various animals, including a flaming bird or a fish that shoots bullets.