Sharing of meta data of all existing songs and the one currently listened to between all users of mobile music players (e.g. mobile phones) in a certain area like the bluetooth range.
This also means sharing personal information about music taste, current mood (determined by the current song which one is listening to at the moment) and so on.
If you like to listen to a song you can use the 30 seconds limit for free listening to do so.
If one is interested in getting the song of another person there are several ways to do this: Direct exchange is only possible if the rights allow this transaction, otherwise there could be the possibility to directly link to an online shop offering this song, which then can be downloaded via the mobile service provider.
There could also be the possibility of public "music terminals" broadcasting their playlists and music, so that personal and commercial interests can be mixed (-> important for promoting new songs!)
Furthermore the social interaction between people in public places can be increased. There could also be "games" be done by this, like to guess a song by any few seconds of it. Or people get a signal/a note every time they listen to the same song (in this case without knowing what the other does at the moment!)
Another interesting information to exchange here are song ratings or listening counters.
The sharing of all the meta information is to be fully controlled by the users, so that they could keep privacy as they want.
This could also be interesting for parties: Instead of one person to organize all music and then to react on people's request, the central music player connected to the stereo can use the meta information and the music of the different music players of the party guests!
Idea for project name: OMMDEX - Open Media MetaData EXchange