Tree 2.0

Tree 2 is an outliner featuring a horizontally expandable tree view. Tree assists you in organizing your information, sketching plans, and brainstorming new ideas.

Tree allows you to store your ideas and keywords in segments that you can sort, re-arrange, and constantly refine. Tree is designed to be a lightweight application that lets you concentrate on your ideas.
If you don't like the Mac App Store, you can purchase Tree directly from the developer by requesting a special purchase page. (See Contact at the bottom of the page for instructions.)