In perusing PIM-related Yahoo groups, I found a link to a Lotus Notes-like PIM. One of its free plug-ins is a tree-type Organizer/PIM. And at $30, it may be a true bargain. However, there has been no update since Version 1. was released on Aug 29, 2003, so it might be buggy or may not have updates. Anyway, here is the Web site.

http://www.pimentoworld.com/