Developer Amplitude Studios' Endless series of strategy games, including Endless Legend and Endless Space 2 (but minus its predecessor, for reasons which will later become clear), is free to play on Steam until next week.
Amplitude's free weekend, which coincides with the launch of new expansions for Endless Space 2 and Endless Legend (titled Penumbra and Symbiosis respectively), runs from today, January 24th, until Monday, January 28th. During that time, the aforementioned Endless titles, plus Dungeon of the Endless, will be available to play for nowt.
That's not quite the end of it, however. Pretty much the entirety of Amplitude's back-catalogue is currently discounted on Steam, meaning that you can continue your strategic adventures for significantly less than the usual price once the free weekend is over.