I can remember time when Internet was still young and the basic mean of communication was e-mail. Real-time chat was possible through IRC protocol. Later, changes came with the appearance of Instant Messaging (IM) apps, from which ICQ was probably the first. There were many of them, all having similar, basic functionality - list of contacts, seeing their status (available, away, offline) and chat. Gadu-Gadu (renamed later to GG) was local one very popular in Poland, but others were also in use, like AOL, MSN, Jabber.
Over time clients for those networks became bloated with more or less useful features, fancy skins and emoticons, and of course lots of ads - which all consumed additional RAM and CPU time, not to mention just being annoying. Then, something wonderful happened - alternative clients started to appear. Whether based on open protocols (like Jabber) or reverse-engineering others, these multi-communicators were often lightweight, supported alternative platforms (like Pidgin working on Linux) and integrated support for many protocols in a single app, with single list of contacts and unified user interface. My favorite one was Konnekt and later AQQ.
New era started probably with Skype, which for most of us was an introduction to new features like audio- and videochat. Next generation communication apps became more complex, provide more useful features, but at the same time they are even more resource-heavy and (in case of smartphones) drain battery. For some reasons they have no alternative clients (probably because their protocols are more complex, proprietary, and encrypted). And there are many of them. So here I am today, having multiple messaging apps installed on my smartphone. I do most of chatting with my friends via Facebook Messenger these days, but some of them prefer other program, so I ocasionally use also: Skype, Telegram, WhatsApp, Signal, Slack, Google Talk and Hangouts, plus of course the old good phone calls, SMS, and e-mail. What a mess!
At the same time I can see they all start to converge. They look similar as it becomes more and more clear what's the optimal user interface for such app. Features added to some of them quickly appear in others, like end-to-end encryption or (most recently) commenting others' messages with a smiley. So I think the future is once again to have a single messaging app. I only hope it will be just a GUI supporting multiple protocols, and not one of those "Big Brother" corporations (who already know everything about as) dominating all the messaging, just like Gmail dominated market of e-mail servers and readers.