Yammer

Yammer allows work colleagues to communicate, collaborate, and update each other with microblogs.

Yammer’s user base has been growing rapidly since launch in late 2008, and the service is now used at over 100,000 companies world-wide. The company took top prize at TechCrunch 50 in 2008 and has been featured in the New York Times as one of the “9 sites IT pros should master in 2009.”