Geneva - An all-in-one communication app for groups & communities

Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.

SwearJar - A Slack bot that donates money to charity when you curse

Eventbrite - Discover Great Events or Create Your Own & Sell Tickets

Seek a Guru - Monetize your knowledge through mentoring

Calendify - Calendify is an event community where you can share, publish, and subscribe to event calendars. It helps you to stay informed about what you are interested in and what is yet to come.