< * http://acs.ist.psu.edu/projects/dismal/dismal.html
> * http://elpa.gnu.org/packages/dismal.html
The introduction warns against bugs and missing features, but this is certainly the one which has been around the longest. It is no longer in hugely active development, but I (FER, 29/dec/08) am still around to answer questions. There is a manual and some example uses of it have been published in conferences and also in a journal. It is also part of the Emacspeak (audio interface) desktop http://emacspeak.sourceforge.net/applications.html
You would be very welcome to merge it with another spreadsheet, or take over development.