They claim to be leftist but everything I have ever seen from there is just pure unmasked Nazi shit.

Apparently (this is all from their wiki so grain of salt) it's a forum descended from the facepunch forums (formerly run by the guy that made garrys mod).

I think they also host video game servers for old valve games.

Where politics comes into it idk but it seems very typically liberal (up to and including describing themselves as leftist), and I'm guessing that just reflects the general consensus of the user base, plus is probably partly in response to frequent exposure to the utter abrasiveness of gamer chuds and 4chan types.