Dropbox bought this founder's buzzy workplace chat app for an 'unreasonable' amount in 2014, but then abandoned it as open source. Now, he's relaunching it with a ton of new features

· Tim Abbott sold his buzzy workplace chat app, Zulip, to Dropbox for an "unreasonable amount" in 2014. 
· At the time, Dropbox wanted to reinvent the entire workplace productivity suite and had just acquired email startup Mailbox, too. 
· But about two years later, Dropbox abandoned that strategy to refocus on its file...