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Slack is letting you chat and collaborate with employees at other companies

  • Shared channels will let existing Slack users more easily participate in discussions at other companies.
  • Slack said it has more than 50,000 paying teams and 2 million paying users.
Stewart Butterfield, co-founder of Slack and Flickr
Mark Neuling | CNBC
Stewart Butterfield, co-founder of Slack and Flickr

Slack, the messaging app that's exploded inside companies, is now focused on making it easier for users to collaborate with people at other businesses.

On Tuesday, Slack introduced a feature called shared channels. CEO Stewart Butterfield told CNBC in an interview that it's the most important thing the company has released since the Slack app became available in early 2014.

"It's deceptively simple in concept and very difficult and complicated in execution," Butterfield said.

While Slack as a communications tool has become exceptionally popular in businesses of all sizes, the company faces competition from some of the world's largest tech brands. Microsoft has been adding features to the Teams communications app it introduced in November, and Alphabet's Google introduced Hangouts Chat in March, although it is not yet widely available.

Facebook also has a product called Workplace, which is more like the consumer version of Facebook but for businesses.

Slack's shared channels product is currently available in beta. The idea is to foster collaboration in a single place among people who work at different companies or on different teams, eliminating endless emails and making it easier to search within conversations.

Slack said it has more than 50,000 paying teams with 2 million paying users and is generating more than $200 million in annual recurring revenue.

Slack is also kicking off its first localization effort. French, German and Spanish versions of the app are available now and a Japanese version is on the way.