Dialog Messenger - handy and feature-rich enterprise multi-device messenger available for server or cloud – Slack-like, but not Slack-limited
FullCalendar - FullCalendar is an open-source JavaScript event calendar.
Ripcord - A desktop chat client for Discord and Slack
Letsfind - Letsfind is a fast, easy-to-use, ad-free way to create online (meeting) polls.
Done Hui - No need to switch between multiple pieces of software to get through the workday. CHATS: Communicate freely. CALENDAR: Know your team's availability, plan meetings. No more conflicts. TO-DOs: Stay on top of all projects. FILES: All files, one spot.
FreeBu - Smart free/busy calendar sharing and meeting organizer.