For $12 you can chose 9 games - check your emails or sign up for the newsletter and you should receive a discount link. If you don't you can still have it for $15 for your choice of 3, or $20 for your choice of 9.
The available choices this month:
Age of Wonders Planet Fall Deluxe Edition
Battlestar Galactica Deadlock Season One
Beat Hazard 2
Don't Escape 4 Days to Survive
Several good choices, little bit of fluff.
Grotto as a DRM free bonus
Popup Dungeon Sneak Peak
and they're going to throw in a mystery bonus game at the end of the month.
All games work with WIndows, some work with Linux and Mac. Some of the Windows only games will still work with Linux with Proton enabled.
Per HangryCheeto -
If you're not a subscriber, check your email and your humble account. They are running a $12/month subscription special right now, so you should be about to get
9 choices this month for $12.