Heap Analytics and Fullstory are two popular systems (among others) for this sort of thing. They record and instrument your user sessions much more comprehensively than GA does.

Multiple ways.

Using just your database, you can store records when users complete certain actions.

Eg. When a contract is uploaded, modified, when new people are invited to collaborate over it ...

That way you simply query for user actions over a period.

I use Google Analytics to do the same thing via events. Fire events when actions take place, review the data in your dashboard.