Quake Champions is free on Steam in a limited promo which ends June 18th at 10AM Pacific Time so make sure to add the game to your account by then.

Quake Champions
For a limited time you can join the arena for FREE. Download Quake Champions on Steam or Bethesda.net Launcher between June 10-17 and get instant Early Access. If you log in during this time, you can stay and continue to play even after the event is over! Play solo, with friends, or against the all-new bots in classic modes like Deathmatch, Team Deathmatch, and Instagib; or put your skills to the ultimate test and compete in Ranked Duel and 2v2 modes!

Go to Steam.

Ziggurat
You can also get Ziggurat for free during the GOG Summer Sale. The giveaway lasts 48 hours until June 13, 1 PM UTC. Dungeon-Crawling First Person Shooting at its finest! Fast-paced combat! Dozens of perks, spells and enemies! Level ups! Random Dungeons! Traps! Badass bosses! Carrots! Ziggurat is the best combination of First Person Shooter and Rogue-LITE you have ever seen. The game focuses n fast-paced first person shooting, with an old-school vibe, and updated handling and game mechanics. Dungeon crawling and RPG/Roguelike elements are added into the mix, resulting in a fun, challenging and varied game, with lots of content to discover.

How to get Ziggurat DRM-free version for free: Just head over to GOG and add the game to your cart and checkout. Simple as that.