Here's The App Marc Andreessen Was Raving About On Twitter Yesterday

A new business app from one of the founders of Flickr is getting a ton of attention today, and for good reason.

It's called Slack, and yesterday it got a major shoutout from Marc Andreessen, the powerhouse venture capitalist that mega firm Andreessen Horowitz is named after.

In a tweet, Andreessen posted a chart pulled from an update deck from Slack itself. It shows the number of daily active users for the app since its August launch, and the growth is phenomenal: after a brief drop as users took time off for the holidays, the number of users has exploded in 2014.

As Andreessen puts it in his tweet: "I have never seen [a] viral enterprise app takeoff like this before - all word of mouth."

Business Insider got a brief overview of the desktop app from Stewart Butterfield, CEO of Tiny Speck and co-founder of Flickr, when it launched back in August. Since Andreessen's chart showed that most of Slack's users are mobile, we thought it would helpful to show what it's like to use the iPhone app.