Yammer, Inc. is an enterprise social network service that was launched in September 2008. Unlike Twitter, which is used for broadcasting messages to the public, Yammer is used for private communication within organizations or between organizational members and pre-designated groups, making it an example of enterprise social software. Yammer originally launched as an enterprise microblogging service and has evolved to become a full-fledged enterprise social network.

Access to a Yammer network is determined by a user's Internet domain, so only those with appropriate email addresses may join their respective networks.

According to TechCrunch in September 2010, the service is being used by more than three million users and 80,000 companies worldwide, including 80 percent of the Fortune 500. In a late April 2010 interview, Yammer CEO David Sacks said that Yammer revenue was doubling every quarter, but would not disclose 2009 revenue beyond describing it as "seven figures". Sacks also said that 70 percent of Fortune 500 companies were using Yammer at that time.

David Sacks is a television writer and producer. His writing and producing credits include The Simpsons, 3rd Rock from the Sun, Malcolm in the Middle, The Tick and Murphy Brown. The only Simpsons episode Sacks has written is the season six episode "Fear of Flying".

Born and raised in New York City, Sacks attended Harvard College, graduating with a degree in Government in 1984. While there he began his comedy writing career as an editor of the school's humor magazine, The Harvard Lampoon. Upon graduating, Sacks moved to Los Angeles and began writing for television.

David is the co-founder and Senior Lecturer of The Happy Minyan of Los Angeles.

He is the founder of the Jewish Impact Films fellowship with television writer Jason Venokur and Speeddating creator Rabbi Yaacov Deyo.