One license makes networking applications sources available if modified, the other doesn't as far as I'm aware. Not sure why it has 3 "licenses" they really should figure that out. I think they should just say they're AGPL if anything and make any exception a paid license that turns Mattermost into MIT or Apache license or something? But having two licenses is fine, or one license and exemptions, but three and an exemption that doesn't really make sense... Sheesh.