This has also been discussed a fair amount on at least one OpenOffice.org mailing list. I've thought about it myself. I think the question is not "why aren't there any," but "why aren't there any yet."
OpenOffice.org folks and anyone else who thinks this is a good idea -- come on in, the open source is fine. : ) That is to say, there isn't one now that I know of, but I have faith in the Open Source community to spawn one quite quickly.
This was first published in November 2003