Still don't own Outlast? Outlast Deluxe Edition is currently going for nothing on the Humble Store and it supports Linux.
About the game:
In the remote mountains of Colorado, horrors wait inside Mount Massive Asylum. A long-abandoned home for the mentally ill, recently re-opened by the “research and charity” branch of the transnational Murkoff Corporation, the asylum has been operating in strict secrecy… until now.
Acting on a tip from an anonymous source, independent journalist Miles Upshur breaks into the facility, and what he discovers walks a terrifying line between science and religion, nature and something else entirely. Once inside, his only hope of escape lies with the terrible truth at the heart of Mount Massive.
Outlast is a true survival horror experience which aims to show that the most terrifying monsters of all come from the human mind.
It's easily one of the scariest games I've ever played! Seriously, I can't get very far in it as it really is frightening.
Our streamer will likely be doing the Outlast DLC for Halloween on our Twitch channel which should be a lot of fun.
You've got another 1 day and ~8 hours to grab it for free for the Humble Store.