Easy to use and every feature which are in there is on point. A very great way of communication. Mainly on smartphones. Very lite and responsive. I think at this point everyone knows this. If you don't then come out of the cave. And it's popularity have grown when many crypto companies used it to communicate and for announcements.
There's other one too. (Telegram)
I guess we can put them in the same category, but DISCORD is better TBH.