Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Classy - Expressive, flexible, and powerful stylesheets for native iOS apps
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Little Green Light - Illuminating Data. Advancing Nonprofits.
Bylde - Bylde is a SaaS platform you can use to Start, Manage and Grow your groups and communities.
Agilon One - Agilon One is a Nonprofit CRM software solution that connects and gathers information on constituents.