How about a combined backup/sync solution for Excel spreadsheets? The sync portion could work like Dropbox, but the daemon would only pay attention to Excel files on a given machine, or in a folder, like a user's home directory. There would be a company account on a website or a locally running web appliance, where users could share spreadsheets, particular pages in a spreadsheet, or even particular cells. This would be combined with an Excel macro that can pull-down such shared data from the account website. Updates to data would only be sent when the spreadsheet is saved and uploaded by the local daemon.

This could even be automated by screen-scraping Excel running on virtualized Windows instances.