iFreeTools Creator, which I am working on, is moving in this direction.

Interestingly, I did not start out to build a replacement for Excel, but to offer customization features for my CRM app. Removing the default CRM entities (or "tables", if you would like to call it that), provides a slate wherein you can build your own custom database apps.

Like, a bug-tracker : http://blogs.ifreetools.com/2010/03/building-simple-bug-trac...

Or, may be, a property management app : http://blogs.ifreetools.com/2010/01/build-apps-online-over-g...