Rui CarmoI used this for a good while nearly nine years ago. And now, out of the blue, I find out that they went Java and have both Mac and Linux editions. Well worth trying out, even despite their choice of language.
Update: It is as nice as I remember it, but takes up a lot of resources and (this bit I had forgotten about) breaks one of the cardinal rules of document formats: It creates both a document and a folder to go with it, without even wrapping them in a Mac-like bundle. Might work OK with iDisk, but is a nuisance to manage and as such a major put-off, even if the app makes it easy to exchange zipped versions of the set with other people.