I was on USENET from '89-2005-ish, on various Unix versions. I used trn until strn came out; it has an amazingly useful threaded display, where you can move around posts on a big branching thread to follow replies. strn added scoring, so a file full of rules would up and downvote things (privately) so I'd only see the good stuff up top, and never see a lot of obvious garbage.
There were less capable clients for Windows & such, but if you had the choice you used a text-mode Unix client.
September That Never Ended wasn't great, AOLers were really terrible, but now the entire Internet is AOL-quality, so I doubt it'll make much difference.
Swords & Wizardry my review of Revised - OD&D rather than B/X which is very cartoony. Much more, uh, complete than White Box, much simpler than AD&D, really a great sweet spot.
Advanced Fighting Fantasy, Troika!, etc. - great simple game, minimalist rules, setting-as-system in Troika's case.
Monsters! Monsters! is replacing Tunnels & Trolls, which has been bought & sold a couple times now and is in limbo. M!M! runs all the T&T adventures, esp. the solos, and is a great pick-up game.
I love the adventures for Lamentations of the Flame Princess, but the system's been neglected, the Referee book is still not out, there's no monster book, etc. But the adventures work in any OSR game with minor tweaking.