Google Docs, Calendar, and Meet.

I put it all together on Google: Docs for the single source of truth, Calendar for scheduling, and Meet for meetings. Everybody has a Google account, so it's just easy. It takes seconds for anyone to get in.

Google Docs

You can see people's changes in real time pretty well, and there's version history you can look back through.

Google Calendar

Whenever I add a meeting to the calendar and add people to it, Calendar automatically creates a Google Meet and generates the link, so I don't have to do anything else.

Google Meet

I use Meet because it goes hand in hand with Calendar.

I also attach the Google Doc to the meeting. When people click on the calendar invite, they can open the doc we'll be referencing throughout the meeting before they even join.