https://www.pcgamer.com/guns-of-icarus-alliance-and-galactic-civilizations-2-are-free-on-steam-right-now-and-you-get-to-keep-them/

If you're looking to plug a few hours this weekend but don't fancy splashing out on something new, then you're in luck, with two games going for free on Steam right now that you can download and keep forever. 

The first is Guns of Icarus Alliance, the expanded version of steampunk airship combat game Guns of Icarus Online. The original was purely PvP, but Alliance adds PvE elements, six factions to choose from, and an ever-changing world "that is constantly being shaped and reshaped by the players".