Telltale Games-First Episodes Free Only iOS only
I know this occurs on occasion but some of the first episodes of the telltale games are free.
Of note, Hector episode 1 has never been free. The remaining games of each series also seem to be discounted.
For iOS (most of them only for iPad).
The appshopper link above will list all of them.
Series include: Back to the future, Sam and Max, Hector, Monkey Island, and Law and Order
Back to the Future Ep 1:
Monkey Island Tales Ep 1 HD:
Monkey Island Tales Ep 1 (iphone version):