Out-of-band data Java socket implementation
geocitiesarchive.org
geocitiesarchive.org
Those groups have been on a long-term decline, but it's been very slow, and there's still the occasional thread with substantive content as good or better than you'll find anywhere else.
I'm still subscribed to sci.crypt but that group sadly succumbed to crackpots and spam several years ago. There may still be some experts lurking but it's hard to see through the noise.
I absolutely hate web-based forums, so you can pry Usenet (and tin) from my cold, dead hands. HN would be awesome with NNTP access.