There’s no real explanation why Saira is currently free on Steam, but it is. This means that it’s some sort of mishap and it won’t stay free for long. So, just in case, go download it now. Even if it is planned, it still means you get a free game. Maybe an announcement will soon follow, but normally the game sets you back $9.99
Saira, from the maker of games like Knytt, is a puzzle platform game with some spooky alien vibes. You’ll run around a differing series of environments, trying to find your way through. It has a bit of a Metroid atmosphere, certainly given its non-linear progression.
You can download Saira for free here.