Microsoft appears to be working on a Universal Windows 10 version of its Paint application. First spotted on Twitter by WalkingCat, the Universal Windows 10 Paint app was under the name "New Paint," and now is named "Newcastle" in the Windows Store. Newcastle is unavailable to download, but the app listing is still present and just gives you a quick history of Newcastle United Football Club.
MSPowerUser was able to download and do a quick hands-on of the Universal Windows 10 Paint app. Paint might be a part of the Windows 10 Anniversary Update due out later this summer, or it could just be an effort by Microsoft to make all its other Windows desktop applications into Universal Windows 10 apps. As other users point out on Twitter, XPS Viewer, Windows Fax & Scan, Microsoft Character Map, and Wordpad are listed in the Windows Store but are not yet available to use.
Presumably, the Windows 10 Paint Universal app will have the same photo and art editing features of the Windows desktop app version. Although the Paint app is not available for download anymore, here is the Newcastle app listing in the Windows Store.