Atari Age is a great forum, not just for Atari machines either. There's still a lot of hardware and software development for Ataris. Also you might want to check out:
- ANTIC the Atari 8-bit podcast https://ataripodcast.libsyn.com/ (part of the fun here is when those interviewed find out people still use the machines today!)
- Floppy Days podcast https://floppydays.libsyn.com/
Both have a lot of interviews with people that worked on Atari hardware and software for ANTIC and all sorts of vintage machines on Floppy days. Randy Kindig, one of the hosts, leads the Indy Vintage Computer Club here in Indianapolis, hopefully are meeting this weekend doesn't get snowed out!
There's also gobs and gobs of stuff, contributed by one of the hosts for the podcasts above, to Archive.org