Flock Trips - Bachelor parties planned, organized, and squared away
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Clearbit for Slack - Send all signups directly to a Slack channel
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Party On Demand - Have a party delivered to your door in 60 mins or less.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.