There is only one file type that uses the .WA extension:
Windows Addon Archive
Addon archive created and used by Win Toolkit, a lightweight application for Windows 7 that allows you to customize a Windows installation; contains application information that can be integrated with a .WIM file to allow you to customize the programs that are installed during the Windows installation.
To integrate a WA addon file, double-click "AIO Integrator" from the Tools Manager, select "Add Addons," and choose your WA file(s).
NOTE: In order to use WA files, you have to download the Win Toolkit, which is able to integrate addons, drivers, updates, gadgets, language packs, theme packs, and registry tweaks to customize your Windows installation disk.
Updated: January 8, 2015