Oh yeah, Powerpro! Wow, that brings back memories...
That is actually the app that prompted me to create NextSTART. Me and John T.Folden couldn't get PowerPro sub-menus to emulate the NeXT OS look properly (although it was ok for the main menu), so I wrote a small app that would pop up a NeXT looking sub-menu when one clicked on a PowerPro menu. Since we wanted different sub-menus for each button in the main PowerPro menu, I also came up with the user-definable hotspots concept (where you attach an hotspot to an app or a window and then define the clickable area in that window that activates the hotspot). Since I'm a firm believer in choice, I also made my simple menu app skinnable from the get go (although it looked by default like a NeXT OS menu).
Eventually that small app became NextSTART, and marked the begining of Winstep, over 10 years ago. 