Total Organizer - Free Personal Information Manager
Total Organizer is a free Personal Information Manager (PIM) which makes it easy for you to organize and plan your business and personal life.

It allows you to store all of your personal and business contacts, tasks, text notes, and to-do lists grouped into various categories. In addition, each item (be it a note, task, contact ,etc) may belong to several categories (tags).
So, this is a combination of folders (tree) and tags. Note, that if you create subfolders (subcategories) - then by opening a folder you can see all the items belonging to it, and the contents of all its subfolders. So, by opening root folder (at the top), you can see all items of given type (e.g. notes, if you’re in “notes” tab)