Public - Group chats.
Teachable - Create and sell beautiful online courses with the platform used by the best online entrepreneurs to sell $100m+ to over 4 million students worldwide.
nocnoc - Instant group chat invite via link
Clever - syncing between education applications for K-12 schools
Viber Communities - Group chat with up to 1B members, admin controls and more
Claroline - Claroline is a collaborative eLearning and eWorking platform.