I have no love for Valve, but I don’t think it can be argued that SteamOS and Steam in general helped jump start linux support for games. I think linux support was always going to increase but I don’t think it was a given that there would be so much widespread support at this point.
No one has mentioned metafilter yet??
Its like a reddit that never acquired enough critical mass to become huge and attract shitty people but at the same time attracted enough people to become its own stable little community.
I particularly enjoy that there is a tradition of making high effort posts where people link together several links on a topic/news story into a paragraph about it. Posts often feel like interesting mini blog posts about a topic rather than just a short description and link and I often find myself learning really interesting things reading metafilter.
It is full of generally left leaning people and the site is maintained by paid moderators so I have never run into toxic bullshit there.
Also I think to make an account to post you have to make a one time payment of $5 or so to discourage people from joining who don’t actually want to be there (and discourage trolls).
https://www.metafilter.com/