Released in 2014, Child of Light was a charming sidescrolling RPG developed by Ubisoft Montreal and directed by Patrick Plourde of Assassin's Creed 2 and Far Cry 3 fame. Ubisoft is currently giving it away, and if you grab it before March 28 you'll be able to keep it forever.
The game's art style is its defining feature—when Andy reviewed it upon release he found it to be wonderfully polished but "thimble-deep", so don't go in there expecting to deliberate for hours over diabolically complex encounters. But do expect a good time: you can't argue with the price.
There's quite a lot of software being offered up for free at the moment. Drawful 2 is a jolly good local party game that you can download for free until April 11, but if you'd prefer to make your own games, these Unity tutorials are free.