Ever heard of Arx Fatalis? Well, it was the first game that Arkane Studios ever made and it is free on PC right now. The company is celebrating its 20th year of existence and this giveaway is a great way to thank the fans for their continuous support.
There are two things that need to be mentioned in that regard, though. First of all, the only way to redeem your free copy of the game is to sign up for the Arkane Outsiders email list. Second of all (this is crucial) - once you claim your free copy, you can only play it via the official Bethesda launcher. Some people may not care about this detail so much, but for others, it can be a deal-breaker.
If you're fine with the offer as it is, you can claim your free copy of Arx Fatalis here. The offer ends on May 31, so you have two days left to do so.