TreeSheets is a mashup of many different program types including spreadsheets, mind mappers, outliners, PIMs, text editors and small databases. It has a tabbed interface and is lightweight and fast, using few system resources even with large files.
It’s like a spreadsheet, 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. It is capable of many kinds of data organization, including todo lists, calendars, project management, brainstorming, organizing ideas, planning, requirements gathering, presentation of information, etc.
Functional in 64-bit and cross platform (Linux and Mac).