Meetingbird - Powerful meeting scheduling and notes — right in your calendar
Briar - Secure messaging, anywhere
Standuply - Run daily standup meetings and track your metrics in Slack
Chat Offline - Last week, and after logging about 100 hours on Apex Legends, Origin started to do me dirty by showing "Chat offline" this results in not showing my friends list in game and me not being able to join them for a game as a result.
Superpowered - Power through the day without your calendar
The Serval Mesh - It works by using your phone's Wi-Fi to not communicate with other phones on the same network.