Car sharing and carpooling have proven to be an effective solution to reduce the amount of running vehicles by increasing the number of passengers per car amongst medium/big communities like schools or enterprises. However, the success of such practice relies on the community ability to effectively share and retrieve information about travelers and itineraries. Structured overlay networks such as Chord have emerged recently as a flexible solution to handle large amount of data without the use of high-end servers, in a decentralized manner. In this paper we present CarPal, a proof-of-concept for a mobility sharing application that leverages a Distributed Hash Table to allow a community of people to spontaneously share trip information without the costs of a centralized structure. The peer-to-peer architecture allows moreover the deployment on portable devices and opens new scenarios where trips and sharing requests can be updated in real time. Using an original protocol already developed that allows to interconnect different overlays/communities, the success rate (number of shared rides) can be boosted up thus increasing the effectiveness of our solution. Simulations results are shown to give a possible estimate of such effectiveness.