FeatureServer is an implementation of a RESTful Geographic Feature Service. (What is REST?) Using standard HTTP methods, you can fetch a representation of a feature or a collection of features, add new data to the service, or delete data from the service. Use it as an aggregator -- post your GeoRSS feeds to it, and then browse them using WFS. Use it as a translator: use the OGR DataSource to load a shapefile and open it in Google Earth. Use it in any way you like.