I'm building a spreadsheet app - http://gini.io. It's a project I started last year, then stopped working on it and now am back on it.
The key differentiating features right now are super easy importing of data from web apps and doing joins between sheets.
The basic free personal plan is live now, but I'll be adding paid plans for businesses over the coming weeks. Please give it a spin and share your feedback! - http://gini.io
I would love to see some screenshots on the homepage, such that I can get a feel for the product. I think that might also encourage more people to sign up.
A cool idea would be a really easy to use API as I know a lot of people have issues with the GDocs Spreadsheet APIs. Have methods such as 'appendRow' and make it super simple to push data there and share the sheets, and it has immediate value to lots of people.
The key differentiating features right now are super easy importing of data from web apps and doing joins between sheets.
The basic free personal plan is live now, but I'll be adding paid plans for businesses over the coming weeks. Please give it a spin and share your feedback! - http://gini.io