There's long been an open secret that Slack, the real-time group messaging service, was developing an official app for Windows Phone. We've got a Windows desktop app, but so far nothing official for phones. All has been quiet of late, and following a few teaser images released by the developers on Twitter recently, things are now most definitely progressing.

A beta is coming and some Slack users are being invited to take part in testing.

Here's part of the email that's going out:

"Hey there!

We're nearing the end of an unexpectedly long and winding road towards an official Windows Phone app for Slack. There have been many false starts and discarded dreams — you may have actually used one or more of those attempts! — but we think we have something nearly Slack-worthy for real this time. We're launching a beta of our new Windows Phone app and we'd love it if you'd join us."

This is a beta, so the standard warnings of "here be dragons" apply. This is a roundabout way of saying that we need your feedback, which you can provide by replying to this email or choosing the "feedback" link in the app (you'll find it under Settings -> About)."

Other than that there's no indication on what time frame Slack might be working on, but for anyone who uses it (including the Windows Central team) it's great news.

Thanks to everyone who tipped us!