For game design documents, I use Confluence from Atlassian.
For project tracking, Trello.
Communication depends on the size of the team and the project. In a more professional/commercial project, Slack has been the place. But if I'm doing a personal project with a friend, I usually just make direct contact through Signal.
I use Git currently, even though it might not be the best for heavy game projects. I would love to hear what alternatives there are for smaller indie projects. Perforce I know a lot of bigger studios use.
I do as many video calls as possible (I don't mean to overdo it. This depends on the team and personality types, of course. But perhaps once or twice a week or every other week). A lot is communicated through visual queues that get lost in text or voice. Maybe not for small things where you need a quick answer to a question. But having longer discussions about things, I think video calls have significant benefits. You get a much better sense of soft values. It's not all about data and information sharing; soft values, emotions, and building relationships during the project are essential, too.
