From reading other people's discussion about this, it sounds like there is an API that people access and use, l but it hasn't been officially published or supported, and so could be subject to unannounced changes that break the third-party app. Also there are some security token issues that I think still need to be addressed in a better way, but there is debate about how serious this is in practice.Tesla should provide àn API to allow developers to create apps. Then they could focus on improving the driving experience
It would probably be fair to ask if there is any other car on the market that supports third-party apps through public APIs.