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

EventBrite Online RSVP - EventBrite Online RSVP is a cost-effective event management software that provides services to help businesses organize, invite people together for an event, and sell tickets.

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

Rsvpify Virtual Events - Rsvpify Virtual Events is an event management tool that provides you various functionalities ranging from setting up the entire event to selling the tickets online to the targeted audience.

Bigtent - BigTent is a web-based organization and communication portal for groups.

EventCreate Online RSVP - EventCreate Online RSVP is a tool for collecting RSVPs online.