Flickr creator takes sign-ups for Slack, an office collaboration tool with universal search

Collaboration tools are nothing new, but they don't always make it easy to find what you're looking for: conversations, files and other resources may sit in entirely different places. Flickr co-founder Stewart Butterfield wants to solve that through Slack, a service that just started taking sign-ups for its private preview. The collaboration app centers on a universal search interface that simplifies locating conversations and shared files, even if those files are hosted by a third-party provide...