Facebook is a social networking site that makes it easy for you to connect and share with family and friends online. Originally designed for college students, Facebook was created in 2004 by Mark Zuckerberg while he was enrolled at Harvard University. Facebook also gives options to create public groups. These are often also used as a kind of community. The groups you can create has chat possibility inside a post, but it's seen as one chat with one direction into a subject and is not that organisized for multiple subjects inside one group.
Discord is a voice, video, and text chat app that's used by tens of millions of people ages 13+ to talk and hang out with their communities and friends. Discord offers multiple options for building your community, club, or group. Discord is most chosen because of the extensive possibilities. You can chat, video chat or call. You can have multiple topics under a larger topic. You can work with a lot of roles and can customize a lot with this. Discord community needs more control as time goes on and that requires employees or volunteers who are working on it to provide a nice community.
Reddit is a social news website and forum where content is socially curated and promoted by site members through voting. The site name is a play on the words "I read it." Reddit member registration is free, and it is required to use the website's basic features. Reddit is more like facebook and therefore has the negative characteristic that it can focus more on one topic. Multiple topics bring the community quite chaotic.