At MP3.com we had an amazing intranet that combined some home grown tools with some off the shelf tools. Sitting in our new offices, I really wish I had some of the amazing Gotham tools we had. Our friend Ian is creating an equivalent of Drop Box, which was an internal and external file distribution mechanism to overcome the size issues associated with mail gateways.
The piece that I have been missing the most for coordinating dispersed people is the calendaring tool we used called Ctime. Someone told me Oracle bought the company, and since we are a startup, no thanks for the Oracle licensing fees that I can only imagine. That's why I was really happy when I heard about RSS Calendar. Not only is this cool because it is a free (for now) web available calendaring tool, but it also is a great application of using RSS for purposes other than reading blogs, or reading blogs from my phone. I am certain that there are going to be tons of cool RSS / Webservices concepts that come out in the next year.