+1 for Discord.
Discords onboarding is fantasticly simple.
Simply click the big + on the left, click Create Server or Join Server.
Create Server makes a new one in the region you want. Click Invite People to get a link to share out. Done in 3 clicks.
Other people click that link to join the server, and are only asked to choose a username if they've never used it before. Click, type, click, joined