Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Facebook - Connect with friends, family and other people you know. Share photos and videos, send messages and get updates.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Bylde - Bylde is a SaaS platform you can use to Start, Manage and Grow your groups and communities.
Facebook Events - Facebook Events enables businesses to organize gatherings, manage invitations and send notifications and reminders to their audience.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.