TreeSheets calls itself a "free form hierarchical spreadsheet," that offers the intuitive usability of a spreadsheet or text editor combined with the organizational capabilities of an outline or mind map. From simple to-do lists and calendars to more complex data organization such as project management and requirements gathering, the hierarchical spreadsheet is astonishingly versatile. It is structured as a grid that will be familiar to spreadsheet users, but TreeSheets can also be easily divided into subgrids, allowing for nested organization and endless layout options. Users can change fonts or colors and insert images with a few clicks (also worth mentioning is the availability of unlimited "undo" functions). As evidenced by the simple website design, TreeSheets is compact and uses minimal memory (5MB for the equivalent of 100 pages of text on Windows 7, according to the developer). To see the tool in action and view a sampling of the style and layout options, readers can click the "Screenshots" link. Selecting the "Tutorials" link, readers will find how-tos for three types of learners: an in-app follow-along tutorial, a video, and a written tutorial. TreeSheets is free and open-source and is developed by Dutch programmer Wouter van Oortmerssen.