I'm all for alternatives as long they're based on open protocols and truly open apps -- not some where a corporate entity gets to dictate how many users one may have or how many lines you get to store. It should also be fairly easy to connect to and not every open-source project needs E2E encryption. Matrix is probably okay, but I found it (and the apps) fairly cumbersome.

IRC obviously has its limitations, but it shines as an example of simplicity and maintainability with no corporate strings attached.