Eventbot - A group calendar made for Slack
EventTitans - Top rated event management software
Clockwise for Slack - Tame the chaos of work
Tix - Tix is a state-of-the-art, cloud-based ticketing system that features fully integrated access controls, event management controls, multi-channel distribution capabilities, and a robust reporting suite.
Teamweek - A project management software to help you get the best overview. Plan fast, change plans faster!
Brushfire - Brushfire offers tools for online registration and event management.