[rakoo]

I'd like to add treesheets (http://strlen.com/treesheets/) to the list: it's an offline tree based editor so it naturally has an infinite number of levels of details you want it to have. The format is a (custom) single file so it's easy to backup and share. While all data is in a tree, it is possible to display it as a grid. I'm not using it currently because I don't really need it, but it's the first one on my to-try list.