Discord is a proprietary platform that offers messaging, voice and video calls, and file sharing. For those with privacy or security concerns there are a couple of open source alternatives.
Fosscord
Fosscord is free, open source, and supports self-hosted servers. It offers many of the same features as Discord such as voice and video messaging. It’s also compatible with Discord so you can still message your friends on that platform. Other features include decentralization, end-to-end encryption, and themes. Customize the platform any which way you’d like to suit your needs.
Stoat
Stoat, formerly Revolt, is an open source Discord alternative featuring voice and video chat, messaging, and a customizable interface. Stoat lets you self-host the app through Docker. It runs on most modern platforms including Linux, Android, and Windows, and you can use it as a progressive web app.