VxKex is a set of API extensions for Windows 7 that allow some Windows 8, 8.1 and 10-exclusive applications to run on Windows 7.
To download and install, see the releases page.
After installation, usage is easy: just right click on a program (.exe or .msi), open the Properties dialog, and select the VxKex tab. Then, check the check box which says "Enable VxKex for this program", and try to run the program.
Some programs require additional configuration. There's a file called "Application Compatibility List.docx" inside the VxKex installation folder (which is C:\Program Files\VxKex by default) which details these steps, but for the most part, all configuration is self-explanatory.
If you are a developer, source code is provided as a 7z file on the releases page.
