ASP.NET MVC Custom collaboration site for our company.

We are NOT looking for a full project management site.
We ARE looking for something similar to Basecamp.

Has to use ASP.NET MVC. Has to support a multilanguage approach to the ui (open to suggestions, we will provide the translation).
We are a design firm, so we know exactly what we need but we are open to suggestions on how to get it done.

You may have to work with one person from our team (or not, depending on how things develop).