Sins of a Solar Empire: Rebellion. Great game.
Star Control is their most recent game and is an AMD partner game.
This game however is a good RTS. Came out in 2012 and still getting DLC updates in 2018
Free on Steam till 12/19 1pm.
Geneshift: also free on Steam till 12/19 1pm
Epic game store has Subnautica for free till December 27. It is a beautiful underwater game.