The main windows shows the list of recommended and installed applications, allowing you to select the most appropriate one to be associated with the current file type. Applications are sorted by their relative popularity, and their avaliability is indicated by a little markings on each application icon and color.
Application's availability is determined by looking into its most popular installation folders. If you installed some application into a different folder, it might be marked as 'Not installed'
After choosing the application and pressing the OK button, it will either launch the selected application, or ask you to browse for its executable or visit the download site if it is not installed.
You can change main window's appearance through Settings dialog
You can change file type's icon by clicking on current icon in top-left part of the window
Removing file association
The 'Remove file association' dialog provides you with a few options of removing current file's association. You can remove association to the current extension only or to the whole file type; or you can just disable the association for the current logged in user. Just select the desired option and press OK
Removing association to the whole file type may affect more than one file extension. For example, if you have .jpeg .jpe and .jpg extensions all registered as 'JPEG Image' file type, removing the 'JPEG Image' association will affect all those extensions. But if you remove .jpg association only, the .jpeg and .jpe remains untouched.
On Windows Vista/Windows 7 with UAC turned on, you'd need an administrative access to remove file type associations. The Windows Registry Editor will be launched to perform the required operation.
Cleaning Open With... list
The Open With... list became overloaded with unneeded applications quite often. This option allows you to remove the unneeded applications from the list fast and easy, without searching for their traces in the registry. It provides you with a list of all entries affecting the Open With... list contents, while user-wide entries are marked with and system-wide entries are marked with .
There are many registry entries affecting the list contents, so the same application might appear more than once. While Windows' Open With menu eliminates duplicate entries (as long as their executable pathes are exactly the same), the Open With Enhanced shows all of them, so you can see what you are removing.
Application entries are divided between Extension-specific (affects only the current extension) and Perceived type-specific (affects all the files belonging to this supertype).
Some entries, whose executable path was not found in registry, appear in red. Those entries won't be shown in the Open With menu (although the same application might have extra entries that would be shown) and usually indicates uninstalled application or application that had not registered itself in HKEY_CLASSES_ROOT\Applications registry key. There is no harm in removing those entries, although some of them might reappear if you keep using this application.
On Windows Vista/Windows 7 with UAC turned on, you'd need an administrative access to remove the applications from the list. The Windows Registry Editor will be launched to perform the required operation.