Zoho, the online document collaboration tool, now has an add-on to SharePoint that will allow users to edit documents online, behind the network firewall without having to install separate software. It also allows users to edit documents collaboratively in real-time, though we have a lighter version of that using LiveMeeting.
It’s worth noting that while you edit documents behind the firewall, when they are opened, they are copied to the Zoho server during editing, then discarded. So it is clearly not for secret information, but that information shouldn’t be on an unsecured SharePoint in any case. The main benefit is that, when allowed by the agency, users can edit Office documents, and do that collaboratively, without installing the latest version of Office, though they will still need a Zoho license.
Check out some more details here: http://blogs.zoho.com/general/introducing-zoho-office-for-microsoft-sharepoint