Group Office is an open source collaboration package which gives you shared calendars, a customer management module, email, file sharing and a water cooler. Nah, just kidding about the water cooler. Think of it as a project management thing instead. It’s got a nice clean interface, comes with cool Ajaxy bits and all in all looks like it could be pretty useful for the small business user. The fully supported version costs from €10 per month per user, but there’s a DIY open source version you can download and play with on your own. Worth a look.