The bottom of the article links to the history (individual features) of other IM programs from that era as well like ICQ and Yahoo Messenger.
And for a while, there was also Skype for Business (formerly Lync (formerly Communicator)).
Yeah that was part of the brand reshuffling they did to obfuscate things. Lync was their shitty chat app they tried to convince businesses to use that everyone hated. They bought Skype, renamed it to Microsoft Teams, renamed Lync to Skype for Business, and killed MSN Messenger. When people still didn’t want to use LyncSkype for Business, then they killed that as well, and now it’s just MS Teams.
Fun fact any developer working with the api can tell you, there is a clear distinction between de voip bit and the meeting/chat bit. They haven’t bothered rewriting or integrating it in any way so the Skype for business backend is still very much alive.