Location-based multi-player games are currently being pushed by the industry, one main factor being that highly-accurate positioning technologies like GPS as well as broadband mobile networks like UMTS are finally getting widespread. Nevertheless, generic frameworks for efficiently managing user locations are still missing, which strongly complicates game development. This paper presents TraX, a device-centric framework for Locationbased Services, which especially supports proactive and multi-player services and thus perfectly matches the challenges mobile game development faces today. The suitability of TraX is evaluated by means of VsGolf, an actual location-based multi-player game, which has been developed and tested by students in only four days.