[caw]

I'm not a huge fan of Sharepoint, but I'm pretty sure you can do some basic at least view of Excel files in Sharepoint. Alternatively, you can share the documents out with a read/write lock.

I'm not aware of any other products that support it. You could try out this Stack Exchange answer: http://webapps.stackexchange.com/questions/16072/web-based-o...

[rwitoff]

From that list, etherpad looks like the most promising open source & self hosted solution. We'll give this a shot soon. Thanks.