Rails is often used for next-big-thing social networking but we've used it quite successfully for Intranet applications. Our clients have all been Microsoft centric so we've avoided placing the apps under Apache but created them as windows services using mongrel which has fitted well into a Windows only environment.
In many ways Rails excellent Ajax functionality makes it ideal for intranet applications which often need very rich user interfaces.
Our apps so far have been:
1. End of year staff appraisals
2. Satisfaction survey for students in a college