It is a fact universally acknowledged that a developer in want of quick-and-dirty instant communication with a team must be in need of an old-school chat client. IRC may be the rugged old war horse of online communication, dating back practically to the dawn of the Internet age, but it's simple, platform-agnostic, vendor-agnostic, and just works in a way that so many other chat platforms don't. It's not always pretty, but it's reliable.

Fast forward to 2014: A startup called Slack is raising huge rounds of venture funding (£25 million in April), building huge buzz, and turning its eccentric cofounders into Silicon Valley darlings – all by building an scalable, agency-friendly version of IRC meant for this social, mobile, share-and-share-alike era of instant collaboration.

Slack itself maintains a "Customer Wall of Love" on Twitter that just collates all the positive tweets that wave the flag for Slack. People love this thing, and our colleagues in the tech press love touting how it's killing e-mail and ushering in a new age of frictionless collaboration.

Slack's claim that its users spend ten hours(!) a day in the app is impressive. That comes alongside claims that Slack has 13,000 active teams and an impressive projected £2.1 million in annual recurring revenue and growing after only six months. 

But beyond the hype and the visionary rhetoric, what is  Slack? Why do people love it so much?

The mash-up culture meets digital collaboration

Essentially, Slack built a better mousetrap: Slack's IRC heritage is apparent, as chats are broken down into main channels that can be broken down by topic or department – the two by default are "General" and "Random" but you could just as easily make one specifically for sales, marketing, the company softball team, or anything else, at the whims of the user, IT, or both. 

There have been attempts to build scalable implementations of IRC that offer both a slicker veneer and tight IT controls – Atlassian's HipChat can be seen as a really, really locked-down version of IRC. While Slack's interface is incredibly polished and easy to use across the web, iOS, and browser platforms I tested it with, the basic experience is super similar to HipChat, albeit more customizable – customers can customize everything from the color scheme to the behavior of the built-in chat bot, which can be made to help with everything from onboarding to sharing company holiday calendars. 

No, the secret sauce to Slack is with its third-party integrations and API-centric extensibility.

By default, Slack lets you upload files directly to it, associating those files with a specific chatroom. So if you need to share a presentation with the marketing team, upload it within that channel and it becomes accessible and available for comment by any user in that room. If you want to share it with all hands, it's just a matter of changing a few permissions.

That's nifty, but file-sharing is a core feature of many other collaborative platforms, and it's only the tip of the iceberg for Slack. The real power comes from adding in content from all the other systems that you use day-to-day. 

Many of Slack's third-party integration options come straight from the wishlist of developers, including popular services like Github (code version control) and Zendesk (help desk ticket management). This sounds simple, but the possibilities are profound: When new code is pushed to a repository, everybody in a development team's channel can get an alert. There are tons of options, involving far too many services to list here, but I'll single out the irrepressible, terrible Yo

It's not just for coders, either: Integrations with MailChimp and Twitter mean that a marketing team can get alerted in the context of a chat room when someone unsubscribes to a newsletter and then complains about it on social media. Type "/hangout" and a Google Hangouts video call starts with the people in that call, provided you've configured the integration. Response time goes down, and general situational awareness from having everything in a single hub goes up. 

So yeah, Slack is cool. Where every other platform claws for user retention by trying to let you do more within the app itself (see Yammer and Salesforce), Slack meets users where they live, pulling both their social graph and data from the outside services they're already using into one über-feed that pushes the content together with the conversations around it, with a search bar for just about everything. No wonder people spend so much time in it.

A tech product for tech people

There are a couple of caveats here, though.

First off, Slack is probably not for everybody. While Slack boasts companies like Vox, Urban Outfitters, and Blue Bottle coffee as customers – and, indeed, launched a website to highlight job openings at teams that use Slack  – it's a most natural fit for digital designers, marketers and developers. Those are the people within an organisation whose job requires them to be in front of a computer, making a lot of changes to all-digital assets, all day every day.

A number of digital newsrooms, including stalwarts like The New York Times and The Guardian and new-media darlings like BuzzFeed and Business Insider, have turned to Slack for their reporting teams. Same situation here – these people need to communicate quickly to create and modify digital assets.

For all the hype, Slack only really shines in the specific use-case of teams, likely distributed across geographies, who have to share and act on information from multiple sources really, really fast in order to produce something digital. It's probably not going to make as much sense for, say, a field sales force. Or the HR department. Or retail workers. 

Combine that with the IRC-like design philosophy, and you can see why Slack is getting so much attention. It's perfectly catered toward people already inclined towards bleeding-edge collaboration tools – basically, techies and the tech-adjacent. Not only is it unlikely to kill e-mail anytime soon, it's unlikely to extend outside the IT organization, at least for a while. 

Second, that impressive revenue figure comes from somewhere. Slack's free version is little more than a trial, offering a mere 10,000 searchable messages and 5 external integrations. If you get hooked from that little taste, plans start at $6.97 per user per month, paid annually, which gets you unlimited archival searching, unlimited integrations, and tighter IT metrics and controls. Depending on your needs, that can go all the way up to $12.50/user/month for even deeper controls, priority support, and a bunch of other promised perks. 

The bottom line here is that Slack is a very cool, very powerful, very handy chat tool that makes collaboration really easy and simple across platforms and services. But as ever, let the buyer beware – it's a better mousetrap, but your users may just not be mice. Not that there's anything wrong with that.