Steam

Ring Runner.

The game is mind blowingly well made. Incredible tutorial, fun story, co-op, multiplayer with self hosted servers, customize 14 different integral parts of your ship with 20 meaningful customizations each.

I bought like 20 copies and hand them out to anyone whenever. I got the book for it, which sadly isn't really well written... And kickstarted their next game Pop-up dungeon.

Legitimately best $1 I ever spent on a game and that includes to the moon.