TomTom, GPS is based on linux, and has third party apps you can get.

But really, you probably wouldn't even have to make an App for the tomtom. If you just made a little program to facilitate, the creation of POI files based on task lists, then people could just have a POI category on their tomtom named RTM or something. And in it, it would have all the locations, that you have stored on RTM. And then in the POI details (Which can be VERY LONG) can list tasks for that location)

TomTom already has a feature where you can have it warn you if you are within a certain distance of a certain kind of POI category. So people could just tell their tomtom to tell them when they are near any RTM POI, and then their GPS would actively give them notice that they are near a task they could complete.

There are definitely things to be ironed out -- but this would be a FANTASTIC PRO feature.

FYI: for non-GPSers (POI=Point of Interest) It is how the GPS stores, all shops/police stations/trais stations, etc, etc -- and you can create your own, or get custom packs etc.