OA Worktracker

I am new to Open Atrium and i want to implement the functionality in my open atrium site in which:

--a user of a space can communicate(create request, ask for files or documents etc) with a user belonging to another space.
For example, a user(or employee) from Finance Dept(i.e., space for Finance Department) has a certain request/task to a user from HR Department(i.e., space for HR Department)

--one to one communication between users across different spaces in which files and docs etc can be shared.