NEW YORK—Microsoft today unveiled Teams, its Slack-like chat service. Teams offers the same kind of Web-based IRC-like text chat experience that Slack users have come to know and love, with persistent storage of historic chats, integrations with third-party services, and of course emojis and memes.

Slack has become the darling of millennials, serving as a kind of digital water cooler for idle office chit-chat, as well as a workspace for teams to tackle projects. This is particularly valuable for geographically distributed teams, as it fosters a style of communication that's more fluid and informal than e-mail or conference calling.

Microsoft's first foray into corporate social media was its purchase of Yammer, which offers something along the lines of Facebook for organizations—a virtual noticeboard to broadcast to your team. While this is still ticking along, the IRC-like model of communications is looking like it's going to be the one with legs. There were suggestions that Microsoft might buy Slack, but the asking price (a $4 billion valuation) was likely too high for the amount of revenue and number of paying customers that Slack actually has.

As such, over the last 18 months or so, Microsoft has been building Teams, its own take on the Slack idea. Microsoft's vision is a little different; Teams has threaded chat so that replies can be directly beneath the message they're responding to.

Microsoft is also heavily promoting its integrations with the rest of Office 365; Teams members can be invited to Skype for Business calls, shared documents can be attached to conversations, and services like Power BI can be directly accessed from within Teams. Third-party integration is also possible, with a range of APIs available.

This Office 365 tie-in is perhaps Microsoft's strongest weapon. Teams will be available to everyone with a small business or enterprise subscription to Office 365, making it essentially "free" to tens of millions of customers. The service is available as a preview today in 181 countries thanks to 18 language localizations. It will be released to the general public in the first half of next year.

For a preview product, Microsoft's release looks ambitious. It's doing more than just offering the core chat experience; the company is also shipping mobile clients for Windows, Android, and iOS. The proof of the pudding will be in the eating, but it certainly appears that it will be a well-rounded offering right out of the gate.

Slack's response to Teams has been to take out a full-page open letter-style advertisement congratulating Microsoft on its entry into the space and giving some "advice" about what made Slack successful. This response has raised a few eyebrows—the comments beneath the Medium version of the open letter are broadly unkind—and gives the impression that the startup is already running scared of an 800lb gorilla that's muscling in on its turf.

Slack does retain one big advantage, however: Microsoft has said that there's no free pricing tier for Teams. Slack, on the other hand, can be used for free, subject to certain limitations. This makes it much easier for organizations to try out Slack to see if it's a good fit for their needs.