Ask HN: Which mobile development platoform does Dropbox use?

I am thinking of writing an app similar to dropbox in the sense that it needs access to device file system etc. Does anybody know if dropbox uses native development platforms for creating the clients on iPhone, Android etc. or do they use some platform like phonegap or titanium for this. I think dropbox uses wxPython for writing desktop clients so just wondering if they use something similar for the mobile clients.