rmr is a real trip. There are a lot more people on rmr than on this forum and there is lots of good info posted there. The problem sometimes is extracting the good stuff from the off topic rants, on topic rants, flame wars, vendettas, grudges....gee someone chime in and let me know if I missed something. Still, it's a really good resource.
There is also a binaries newsgroup alt.binaries.models.rockets for photos, etc. Fewer news servers carry this group and not as many messages are kept on the servers due to the size of the posts (no binaries allowed on the other newsgroup).
If you don't have a news server (most if not all ISPs do) you can also go to
https://groups.google.com/ and search the groups (not just these two). The other oddity on the binary group is it occasionally picks up porn due to automatic posters keying on the 'models' part (methinks).
Finally, in case somebody doesn't know it, Rocketry Online
https://www.rocketryonline.com/ also had a HUGE amount of info, including a good reference library (INFOcentral), message boards, auctions, etc.
I frequent rmr and ROL as well. I like this forum because it is more cordial and a has friendly atmosphere. A thread like 'Retro Rockets of the 50s' probably never would have made it on the other groups. They all have their place.