The developers of ΔV: Rings of Saturn are very happy with the bug reports they receive from Linux users:

Despite having just 5.8% sales, over 38% of bug reports come from the Linux community

38% of my bug reports come from the Linux community

There is currently offered a Linux-version to the psychological Horror-Adventure-game Downfall on the steam store.
Sadly, this game does not start for me on it's own. You'll also need the game The Cat Lady from the same developer.

More detailed information can be found in this forum-post.

It's sad to see, that some developers don't test their own games on all platforms on which they are selling.