Tweaked the registry functions a bit. Hadn't worked on this for a week so looked at everything with fresh eyes.

Get-Apps and Uninstall-App are done. Both use the registry now instead of Win32_Product.

Of course, expect bugs. I haven't tested anything yet.
Updated the latest function names in design.txt.
Tested tested tested.

Result is some changes to the registry functions. Uninstall function works in the one case I tested (had to make more changes to get it working). Install function too works for that one case.
Removed a debug output line.
Working on Install-MSI logging features.
Made changes to Install-MSI and Uninstall-MSI based on further testing.

I think I will make these two functions mimic msiexec more closely.
Changes to Install-MSI. Got to test tomm. Added a -Parameters that takes all the remaining arguments on the pipeline.
Worked on Uninstall-MSI (renamed from Uninstall-App to be MSI specific). Mostly copy-paste relevant bits from Install-MSI.
Loads of little changes and bugfixes to the two -MSI functions. Getting better and better!
Minor changes. Cleaning up of the code to make it look better.