There were also cool places to hang out like Yahoo Games or a few of the location based chat apps that were fun to connect to strangers and just chat.
Discord is so walled garden it's awful in this respect.
I also miss the VRML world builders like CyberTown https://en.m.wikipedia.org/wiki/CyberTown
I greatly enjoyed how with XMPP’s in-band registration you could do things like give each contact a unique XMPP address, only to be used with them. You could have unlimited (well, I never hit a limit) accounts, across a load of servers, proxies per account, unique OTR keys per account, etc.
I don’t think the UI has really been surpassed either, tbh. I really wish someone would do a modern rewrite of Pidgin in some memory safe language.
That said, the vulnerabilities in "libpurple" were way over hyped by someone who rightfully got kicked out of the security community. Most of those vulnerabilities were in fact in protocol implementations that are plug-ins to libpurple and not libpurple itself. I know it's a technicality, but hearing this blatant lie get repeated for over a decade is exhausting.