The goal of OpenAddresses is to create an open and free database of geolocated addresses. You can learn more about this project in the Directions Magazine podcast or in the press release.
The ease of use and simplicity of MapFish allowed the creation of this site in a few weeks. The very nice thing is that MapFish provides automatically a complete range of REST services (see here). For OpenAddresses, a powerful Full Text Search has been developped and will be soon integrated in MapFish. On the client side, the usage of ExtJS, OpenLayers and GeoExt was very flexible and proposes an ergonomic UI. This is particularly important in crowd-sourcing efforts because the learning curve has to be very short. Since data are edited, it was also important to facilitate the acquisition work in order to let the user create a large number of addresses in short time, in another word: efficiency.
On the cartographic server side, MapServer is acting as a cascading WMS. This technology allows the usage of whatever open WMS in the world. MapServer will handle the reprojection work if necessary.
Don't forget to add you own address ;-)