Facebook Chat groups: : Great way to communicate with your peers and employees because who doesn't have facebook nowadays.
Linkedin Lookup: : Large companies can connect with their employees through one single source.
Trello:: Boards, lists, and cards enable you to organize and prioritize your projects in a very flexible and convenient way.
Skype:: Best way to communicate as well as to arrange a group video conference with your employees.
These are my personal favourites.If you love working with other sources then do share on this thread