Steam hasn't forgotten about the remaining Windows Phone faithful. It just seemed that way, with folks on Android and iOS getting a mobile app way back in 2012. The Windows Store listing says that you'll be able to use Stream Guard's authentication system, trade and sell items, keep an eye on the game marketplace and remote download and install games to your PC via the application. Just in time for this year's summer sale; how about that?
Windows Central noticed a bit of a peculiarity here, though: This pocket version of Steam apparently isn't a Windows 10 Mobile app -- it's actually a Windows Phone 8.1 deal. At any rate, you can grab the app for yourself and see what other mobile platforms have been using for the past four years.