Earlier in January, $6 billion Aussie software giant Atlassian announced the surprise $425 million acquisition of Trello , a productivity app for project management with 19 million users, making it something of a cult hit. Trello CEO Michael Pryor describes the sale as a “complex decision”: The company had “a lot of interest” in a new round of venture funding to continue its growth, but says that ultimately, he decided that Trello and Atlassian had so much in common that it made more sense to sell.