There were a few brief wonderful years when I had AIM, FB Messenger, GChat, and a few lesser known protocols all in different tabs in the same window.
It's not like they all needed different interfaces; same data, different wire-noise...
I didnt realize I had trillian setup to log all my conversations to file and I found the logs recently when going through a very, very old harddrive. Middleschool me was cringey as fuck
Upsides: I no longer had to care what messenger my friends used, it was all the same to me. Extensible and theme-able which was just the way I liked my software at the time. Growl integration.
Downsides: I made the mistake of installing and using a FFVII-themed sound pack that invoked a Pavlovian response in me every time I heard certain sound effects from that game. Took the better part of a decade after I stopped using Adium to shake that off.
Even people like me that hated MS and AOL had chat clients that could communicate with their networks and Google Talk/Hangouts and MSN Messenger were both great for what they were. At the time I felt like we had lost something important by moving to "push" networks versus e-mail but I'd take those days now in a heartbeat. Maybe by 2030, something like Matrix will have us back to what XMPP was doing and I'll be able to send a message to someone's shitty Teams from whatever Google's fifth chat replacement is by then.
It's even worse when I'm traveling in east Asia and there are like 5 different Korean and several Chinese chat networks in addition to WhatsApp trying to be the next LINE and becoming the one-stop access point for nearly everything. I'm honestly expecting to see a 7-11 integrated messaging network at some point.