Public - Group chats.
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
chitchat - Chat Room with Selfies and Pagers (yes, pagers!)
Event Hunt - Startups and Tech Events Curated By Locals
Slack - A messaging app for teams who see through the Earth!
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets