Microsoft AP Help is the Help engine created for the Microsoft Windows Vista operating system help. Vista, code-named "Longhorn", was launched for public use at January 2007. There were thoughts it could become the next general help engine but this didn't eventuate. I believe it was a variant of MS Help 2.

Note that authoring and creating .H1s help files is for Microsoft in-house and OEM's use only (eg. Hardware manufacturers who need to integrate documentation into Windows Vista help).