Have you heard of NumSum yet? It is a simple online spreadsheet tool. To be completely honest it lacks many features, but the project appears to be on the right track. Another hinderance is that from my understanding every spreadsheet built on numsum is publically available. UPDATE – After reviewing the site it appears they are building a more advanced version that will be available for a fee. This version has no published release date.
I’ve heard rumors that the Sun and Google relationship could result in a free online office suite. More on this available here. Here’s to hoping a fully functional online spreadsheet tool will be released soon.