A preview version of Microsoft's Universal Skype Messaging app for Windows 10 is available to Windows 10 Mobile Insider testers from the Windows Store.
(Thanks to @teroalhonen for the link to the new Universal Skype app betas.)
From the description of the apps in the Store:
"Skype Messaging, Calling and Video 'Preview' is a new way to experience Skype features. It integrates individual Skype features where you'd expect them - Skype messaging into Messaging and Skype calling into Phone apps for the fastest way to make calls and send messages. It also adds quick access to Skype video calling. With Skype built in, you'll be able to reach anyone who uses Skype on iPhones, Androids, even PCs with just a couple of clicks."
In June 2015, Microsoft officials announced plans to discontinue the Modern version of Skype for most Windows devices (with the exception of Windows RT ones) as of July 7. While Microsoft is continuing to offer the integrated Desktop version of Skype, the company is building new Universal Skype applications for messaging, calling and video for Windows 10.
"The Universal Messaging, Phone and Video apps on Windows 10 with Skype built in will run across phone, tablets and desktops," Microsoft officials told me back in June. Microsoft is planning to build these apps right into the Windows 10 platform, and them available to all Windows 10 users in a future update to the operating system, officials said.
Microsoft officials have yet to announce officially the availability of the new beta of the Universal Skype apps. Some are expecting Microsoft to do so when the company releases to the next test build of Windows 10 Mobile for Windows Phone Insiders -- which possibly may happen later this week.
Microsoft released the most recent Windows 10 Mobile test version, Build 10512, on August 18.