As described on their site and this gizmowatch article, it's excitingly close to the kind of 'Dopplr for cultural heritage' or 'pocket curatr' I've written about before:
Visitors to historic cities provide the iTacitus system with their personal preferences – a love of opera or an interest in Roman history, for example – and the platform automatically suggests places to visit and informs them of events currently taking place. The smart itinerary application ensures that tourists get the most out of each day, dynamically helping them schedule visits and directing them between sites.
Once at their destination, be it an archaeological site, museum or famous city street, the AR component helps bring the cultural and historic significance to life by downloading suitable AR content from a central server.
There's a video showing some of the AR stuff (superimposed environments, annotated Landscapes) in action on the project site. It didn't appear to have sound so I don't know if it also demonstrated the 'Spatial Acoustic Overlays'.