Microsoft\Windows\CurrentVersion\Uninstall. There can be some data for programs that do not exist on the system anymore. The last write time is when the application was installed.
Microsoft\Windows\CurrentVersion\Appx\AppxAllUserStore for installed Microsoft applications. Defines between those that were installed for a specific user or system-wide.
SYSTEM hive root node) - those that run a 32-bit mode. Separate sub-keys for different versions of a program.
Classes\Installer\Products - installed using Miscrosoft installer (those with