n application that use Bluetooth to indicate and start proximity interactions - i.e. people within 10-30m of you. You create a folio - like a little web page - that others in your physical location can see.
The website gives more detail:
Nokia Sensor is a spontaneous, sociable application for spontaneous, sociable people. With Nokia Sensor you can create your own personal pages - called a folio - on your phone. Then you can check out the folios of other Sensor users nearby, exchange messages, and share files. (...) Nokia Sensor uses Bluetooth wireless technology, which means that it works within a 'circle' of up to 10 meters around your phone.
When other Sensor phones come within this circle, your phone can 'sense' them and you can see their folios and send them messages. As soon as you step out of each other's circles, you are no longer able to communicate via Sensor.
I like the 'buddy alert' (first picture: "When you buddy with another Nokia Sensor user, you can use Buddy alert which regularly checks if your buddy is nearby, and if so, notifies you about it.") and this scanning thing (second picture: "If another Sensor user is found, his or her folio will be downloaded to your phone and listed in your scan results."):
