What you describe appears to be a class of software known as project management or Gantt chart programs. MS Project is the more commonly known program on the market, but there are free versions that are often as capable, especially if some of the MS features are not required.
From teamgantt.com comes an image of a project involving creating a specific ...
There are some alternative to Zoom:
Google Hangouts (https://hangouts.google.com/)
Google Meet (https://meet.google.com/). I prefer this one.
I think Etar deserves a mention.
Edit: I noticed deleted events (even from years ago) in my .ics export, like you mentioned. I investigated, and initially thought that the problem didn't happen with Etar, so I mistakenly thought Samsung's S Planner was the culprit. However, I tried to reproduce the problem again, and found out that whether this problem ...
As mentioned in the question, that organisation has stopped using Zoom for security reasons therefore I will recommend Microsoft Teams.
Microsoft Teams allows hand raising, file sharing and storage, collaborate live in real time to work on same document. It has recently integrated whiteboard and breakout room functions also. Both free and paid plans are ...
you can do the following things with jitsi
Share your desktop, presentations, and more Invite users to a
conference via a simple, custom URL
Edit documents together using Etherpad
Pick fun meeting URLs for every meeting
Trade messages and emojis while you video conference, with integrated chat.