Celestia Forums

You can find here the now defunct Celestia Matters forum (as an archived site):

https://web.archive.org/web/20190328124518/http://forum.celestialmatters.org/

Added after 8 minutes 15 seconds:
Downloads (just the page):

https://web.archive.org/web/20160824230928/http://forum.celestialmatters.org/viewtopic.php?f=6&t=44&sid=10727a5899d258196d218f6bf53f0c24

Unfortunately, not all the topics are archived; I tried to go to two different topics, and neither are saved.

You have to find the archived version manually. There are a lot of saved versions. Please share the link, if you find it.