A weekly recap of some of the most interesting venture capital deals, funds and start-ups. : Slack, maker of the popular business messaging app, is now worth more than $7.1 billion. On Tuesday Slack said it closed a $427 million funding round, padding its balance sheet as it takes on some of the world's biggest tech companies, including Google, Microsoft and Cisco. Slack is among the most highly valued tech start-ups, and like consumer companies Uber, Airbnb and Pinterest, it has no plans to go public until at least 2019.