A "hierarchical spreadsheet" that is a great replacement for spreadsheets, mind mappers, outliners, PIMs, text editors and small databases.

Suitable for any kind of data organization, such as todo lists, calendars, project management, brainstorming, organizing ideas, planning, requirements gathering, presentation of information, etc.

It's like a spreadsheet, immediately familiar, but much more suitable for complex data because it's hierarchical.
It's like a mind mapper, but more organized and compact.
It's like an outliner, but in more than one dimension.
It's like a text editor, but with structure.

Have a quick look at what the application looks like on the screenshots page, see how easy it is to use in the tutorial, then give it a download (above). A video someone made (on Linux)

TreeSheets is exceptionally small & fast, so can sit in your system tray at all times: with several documents loaded representing the equivalent of almost 100 pages of text, it uses only 5MB of memory on Windows 7 (!)

TreeSheets is free & open source. Enjoy!

Visit this google group for discussion, and news updates / releases. Grab the source code from GitHub, or file bug reports there / feature requests there. The past donations page. contact the author (Wouter van Oortmerssen) personally.