Computer software from the late 90s and early-mid 2000s. Windows XP, Winamp, AIM, MSN Messenger. Software that was customizable, with different themes and tons of options to configure. That kinda stuff. I love looking back at old screenshots from that era.
For me its forums and older websites. What makes me so melancholic is that it seems that people deliberately are destroying and disregarding the old web now.
Interesting take! Which parts you feel are being destroyed and disregarded? I generally agree that communities on the modern web are lacking. Compare something like Reddit (basically "the" forum now) and something like PokeCommunity. Reddit does a lot of things right, but it's nowhere near as good at fostering a sense of community. Even in smaller niche subreddits there's something about the way information is presented that makes everything feel way more transient. Compared to PokeCommunity or other retro-inspired internet forums, where you get a sense that there's a group of real people here that form their own little social structure. Totally different vibes.
That said, Discord servers are as transient as you can get and they're flourishing. So who knows.