Ftype

In computing, ftype is a command-line utility on Microsoft Windows which lists all Registry keys in HKEY CLASSES ROOT which contain the shell\open\command subkey, and prints out the REG SZ contents of the (default) value within these keys. It is an internal command built into cmd.exe; there is no FTYPE.EXE.

Because (default) values in HKEY_CLASSES_ROOT\<keyname>\shell\open\command contain information on how to open file types with registered extensions, this command essentially lists all registered file types, and which executables are used to open them, along with any switches used by the executable.