Classic IM services that still operate

Is there any older IM services that still operate without the need for revival?
I know there’s Yahoo, which is dying, and there’s ICQ.
But what else?

If we go by the mainstream classic IMs, then we’d see that AIM is dead, Yahoo! Messenger will be shutting down around next month (It has since been shut down on July 18, 2018), MSN Messenger is dead, and you already got ICQ on the list of currently-operating IM services.

I know many might not like my final choice here, but I consider Skype a classic IM by technicality, since it was released around the early 2000s and initially came with IM features, according to some quick research I did, so that could be added to the unfortunately very short list of classic IM services that are on their last legs.

wasnt it 2001 that skype released, might of not been a im at that time but it existed

There is Pidgin, and Quassel (IRC).

Those are clients not Services exists from zero years, and the old versions are not frightened of the new functionality and work quite normally.

Also, it’s impossible to play CS with it: when connecting to any server, hl.exe hangs unhindered if among the processes there is a hated magent.exe. The bug is fixed once and for all by deleting the agent. Unexpectedly turns on without your permission the camera, apparently, takes screenshots and collects data into the database.