Hmm. Don't know if there is an option completely outside of an app store. U can use the app store that Tom Tom plans to enable on it's new gps device.
See http://www.electronista.com/articles/10/04/29/tomtom.to.use....
See http://www.electronista.com/articles/10/04/29/tomtom.to.use....
Basically get noticed with the Tom-Tom(more likely because of pre-established intent) and then come up with an app for other devices. Or like I suggest a browser based app( I don't know if this is currently possible, but am sure it will happen soon)