1up Events - Corporate events as a service
Slack Events API - Subscribe to events in Slack via HTTP
Facebook Local - Discover places to go and events happening near you
B12 Bookings - Bookings scheduling software that integrates with your site
Eventjoy - The Easiest Way To Organize An Event
Guestboard - Lead powerfully-organized group events with Guestboard – a modular event platform that gives groups of 10-1000+ people a central space to coordinate, build excitement, and save money. No more crazy email threads. No more massive group texts.