If you've never fought a guerrilla war to liberate Earth from some alien tyrants before, boy have I got some good news for you. 2K is hosting an XCOM 2 free trial on Steam (opens in new tab) (and Xbox One, if you fancy being tactical from the sofa) so you can send the alien overlords packing for free between now and April 30.
It's good timing, as XCOM: Chimera Squad (opens in new tab) is out today. It's a direct continuation of XCOM 2, with human and alien soldiers working together to keep the peace and melt anyone who isn't a fan of this interspecies alliance. It's a standalone affair, so you don't need to have played XCOM 2, but you still should—it's one of the best strategy games on PC (opens in new tab).
XCOM 2 is available for free now, and you'll be able to play until April 30 at 9:59 am PT. If you don't manage to finish your campaign up before the clock runs out—it's not a short game, but I believe in you—then you can throw some cash down and continue where you left off. It's 75 percent off right now, so you can pick it up on the cheap.
Most of the DLC is on sale, too, including the excellent War of the Chosen expansion. It's integrated into the main game, giving you an alien nemesis to deal with and a trio of factions to ally with, each with their own unique skills. It's the best way to play XCOM 2, so I highly recommend picking it up if you enjoy the base game trial.
If you're looking for more freebies, here are all the free games you can grab right now (opens in new tab).