Marble Skies, a 3D platformer that's actually pretty good has officially left Early Access and they're continuing to improve it with big new features.
After adding Linux support back in April, it seems it left Early Access early this month, although they don't seem to have actually announced the full release anywhere I could find.
Recent announcements mentioned that multiplayer has been added, which is missing from the Linux version since it's currently out of date. Sounds like multiplayer is a little basic right now anyway, as they've only added in one mode which has no actual objective so it's more of a proof of concept. From what they said on Steam, multiplayer is all the Linux version is currently missing while they focus on developing that part of it.
- 60 Base levels! + 52 Bonus, Community levels & 9 GOLF LEVELS!
- Arcade style physics - Quick and responsive controls, using your keyboard and mouse, or even a controller mean that every input you make will be accurate!
- Platforming obstacles and powerups - Each new level presents exciting obstacles, and powerups for your marble! Blast your way around with a Rocket, become a gaint with the Super Marble, float like Mary Poppins with an Umbrella, and more!
- Great soundtrack - With 56 amazing different tracks by Stevia Sphere, you will be humming along with them in no time!
- Leaderboards - Get to the top of the leaderboards, and show off to your friends! Can you get the fastest time?
- Controller support - Support for all different types of controllers!
It is a fun game though and it can be quite challenging. You can find it on Steam. It's 50% off until the end of the Steam sale in a few hours.