I love the Element client for Matrix. I use it with my friends and I have joined a lot of communities on there. It's Discord-like, but I personally find it much easier to navigate than Discord. It's free, open source, decentralized, you can self-host if that's your jam, it's got some solid security and usability features, call quality is great, and I've found it to be very stable and reliable. I'm a little biased because I personally don't like Discord, I find the UI clunky and unpleasant to use, but I love using Element. If you love Discord, you will find Element familiar, but you may or may not appreciate the differences.