Punchbowl - A party planning and greeting card website
Mobilizon - A free and federated tool to get our events off Facebook
RSVPify - A powerful and awesomely customizable platform for selling tickets online for your event.
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Online-RSVP.com - Beautiful online RSVP for wedding & other events. Create an online invitation, track your guests responses.
DownToMeet - DownToMeet is a platform to organize, find, and attend group events.