Slack vs Zimbra

Slack is a team collaboration tool co-founded by Stewart Butterfield, Eric Costello, Cal Henderson, and Serguei Mourachov. The company originally raised nearly $43 million in April 2014. In March 2015, Slack signed a deal with investors to raise up to $160 million in a funding round that values the company at $2.76 billion. New investors include Institutional Venture Partners, Horizons Ventures, Index Ventures and DST Global.

Zimbra Collaboration Suite is a collaborative software suite, that includes an email server and web client, currently owned and developed by Zimbra, Inc. Zimbra was initially developed by Zimbra, Inc., and first released in 2005. The company was subsequently purchased by Yahoo in September 2007, According to former Zimbra President and CTO Scott Dietzen, the name for Zimbra is derived from the song "I Zimbra" by Talking Heads.