Discord is an nice application that provide more social features to gamers compared to teamspeak. At the expense of resource usage, we got an app with better user interface, more intuitive and aesthetic. It provided free servers available for everyone to create. It gets you private spaces that you can use for what has been the most common usage of teamspeak and similar apps, speak with friends on a private server.
There are multiple apps today that provide similar features to discord
Root
rootapp.com Nice design, sells like a more performant and less resource intensive app than discord but I’m not so sure about that, they are also selling privacy but it’s not open source so it probably doesn’t have any e2ee conversations
Stoat
stoat.chat Somewhat a clone of discord and it’s nice, less stable but they are working hard on making a good stable system, it’s open source, no e2ee
Simplex Chat
simplex.chat Ok, this is not really a discord replacement, there is no forums, no group voice chat, no screenshare, but it’s a really nice and very private app
Matrix / Element
element.io Not a discord replacement, users can register on different servers, there is some decentralization in the architecture of this app, it’s a federated architecture
Steam
store.steampowered.com Mostly for gaming, there are group voice chats and all kind of forums and game related social platforms and everything is tied together nicely, not sure about e2ee because it’s not open source but maybe there is some kind of encryption