This set includes over 100 shapes for low-fidelity wireframes of any kind. It is versatile enough to sketch user interfaces for desktop applications, websites, mobile apps, and everything in between.
This collection is part of PowerMockup, which you can download here. PowerMockup is an add-in that integrates itself into the PowerPoint window. To install PowerMockup, you will need PowerPoint 2007, 2010, 2013, or 2016 for Windows.
Once you have installed PowerMockup, simply click on the large Download More Shapes button. You can then browse all available collections and download the ones you like.