Lisanna! Welcome back! Great to see you posting again. 
Have you really been gone that long?
This is an off-the-shelf standard forum software called Discord. There is a thread about using it here: The Ultimate Forum Guide (Codes, Trust Levels, FAQ)
It has quirks. The first thing you need to know is that it is very suitable for WoW, because you have to grind rep with it, 
called Trust Levels, to inserts images and links and stuff, but you can do basic posting without that.