Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Bylde - Bylde is a SaaS platform you can use to Start, Manage and Grow your groups and communities.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
CitySocializer - Join citysocializer today to have fun with a new local, social crowd ▫ Make the most of your free time, any time ▫ See what groups are doing together in your city and join in ▫ Get invited out by others to do things that match your interests ▫ Meet …
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.
GroupSpaces - Free Group Website, Membership Database, Listserv Mailing List, Online Group Management Software : GroupSpaces