Humble have announced they're doing a DRM-Freedom Sale from now until July 9th and there's plenty of good Linux titles available.
As the name might suggest, all titles included have a DRM free build you can download direct from Humble themselves. Although, a lot of them do include a Steam key as well.
Here's a couple of interesting picks:
- Eldritch - 90% off
- Prison Architect - 75% off
- Sunless Sea - 66% off
- Keep Talking and Nobody Explodes - 60% off
- Hyper Light Drifter - 60% off
- Tacoma - 55% off
Check it out here if you're interested.