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

Stewart butterfieldSlack co-founder Stewart Butterfield.

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 — which built Slack — 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.

Here's what it looks like when you first sign in to Slack. Rather than having you enter your profile information through dialog boxes, you have a quick chat with a bot.

Funnily enough, it felt like I was able to go through the setup faster that way -- my thumbs are trained to respond to texts quickly.

Once I got that out of the way, I did a quick swipe from the left the see who I could talk to. The app lets you message entire channels of people (basically, chatrooms) or privately message individuals.

You can create as many channels as you want, and organise them by topic or however else you'd like. Business Insider's engineering team has a channel where it posts fun stories from the site.

Search is a major feature in Slack. You can search for a specific term and see when it's been used in public chats or private conversation -- and a few lines from before and after it was used, in case you're looking for a conversation and not just a single message.

Swiping from the right, you can access files that have been shared either through uploads or in chats. By integrating with a ton of different services, Slack lets you see them all in one place, without leaving the app.

You can see who uploaded any file, when, and in which channel.

Files load extremely quickly in Slack, even when you've never looked at them on your current device. I had to try a few times to get this screenshot before the image downloaded.

Slack makes it extremely easy for teams who make a lot of content to quickly get it to anyone who needs to see it for feedback.

If you have trouble keeping things organised, you can use Slack's file management tools for the things that you're working on by yourself, too.

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