New website questions


I’m designing a new website with Joomla 1.7 about financial spreadsheets.
I already sell spreadsheet applications through another website, but I’d like to focus this one a bit more (more technical).

Is there a web application with the power of Excel I could use on my website? It would be interesting to replace a download of a file by access to a restricted area of the site where users could perform the same operations as in Excel. I know about google spreadsheets but a lot of Excel functionalities don’t work there.

Thanks in advance for any help!