Mattermost - Mattermost is an open source alternative to Slack.
Grenadine Event Planner - All-in-one event management software. All your needs in one place: event planning and scheduling, event website, registration, event mobile app, and APIs.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Digitevent - The powerful software to manage your event participants.
Slack - A messaging app for teams who see through the Earth!
B3App - B3App is an event organizing and management platform that helps people throw, run and manage events.