Collaborative software (or groupware) is designed to help people
involved in a common task achieve goals. Groupware are focused on the
usage of applications and collaboration inside teams.
I've tried to make a selection of application we currently have in our
extensions repository. An interesting discussion would be to make
proposals on applications that we currently don't have implemented,
but would be vital in such a flavor.
I encourage you to take a look at the features and give your opinion.