This software developer’s idea of a sabbatical? Starting an all-female investor group during the four-month gap between her previous job as Twitter’s director of product and joining Slack, a $3 billion hyper-hot corporate-messaging startup. During her first year heading product strategy, the number of active users relying on the service tripled to more than 3 million. Her latest project: an $80 million fund for startups that buy into Underwood’s vision of turning Slack into a hub for everyday business tasks like arranging transportation.