A highly anticipated “email killer” is now at large.

Slack emerged out of beta today and introduced a tiered pricing model. Slack is an internal communication tool for distributed teams. It aims to make people “less busy” by bringing all of their communications together in one place.

It was founded by Stuart Butterfield, a cofounder of Flickr, which Yahoo bought for a reported $35 million in 2005.

Slack collects messages and files from Twitter, DropBox, Google Drive, Asana, GitHub, ZenDesk, Mail Chimp as well as instant messages. It integrates their announcements, alerts, bug tracking, and data into the communications stream when and where appropriate.

Teams can then create open channels for projects, groups, and topics and set up custom notifications. Slack also has a search function, tools for uploading documents, and “ambient awareness” of what your coworkers are doing. The system analyzes all of this activity and provides reports on usage statistics.

“We have a real challenge getting organizations to switch, because if it’s consumer software, it’s just one person who needs to put it on your phone, and you use it,” Butterfield told VentureBeat last year. “But when you have to convince 17 people at once, or 35 people, 58 people, and some people come to office pissed off about something that happened … and then their boss comes in and tells them they need to use the new notifications system, sometimes they say, ‘Fuck you!’”

Collaboration remains a significant challenge for companies of all sizes despite the number of startups working on the problem, such as Yammer, Hipchat, Asana, or Basecamp. The trouble is that all of these different tools distribute information across multiple locations, and keeping up with all that activity is just as time-consuming as staying on top of email.

After launching in private beta in August, Slack signed up 8,000 customers in 24 hours. Butterfield told VentureBeat that organizations using Slack during the test period dramatically reduced their dependence on email. Fortune reported that Slack now has 16,000 daily active users across over 1,500 teams. These employees send a collective 2.5 million messages last week, and early customers include Square, Urban Outfitters, and Harvard Law School.

Slack has a free option for “lite users.” From there, it costs $8 per month per user or $15 per month per user depending on your storage needs. It has an enterprise tier planned for next year as well as features for guest access, additional administrative controls, and a “configurable email ingestion service.”

Slack is the first product from Tiny Speck, which has backing from Andreessen Horowitz and Accel Partners.

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