Hmm, I am afraid that if you want a binary format that is cross-platform compatible, you'll have to define it yourself, I do not think there is a standard for such a format.
Well, of course, you may find an existing binary format for data exchange between a given platform pair, or even for a few platforms, but I do not think there is any standard one that is really cross-platform in the wider sense. And there are plenty of quite compelling reasons for that, one of them being that there is not one binary format, but several.
Having said that, some network protocols do define some low level binary formats that you might want to use. But I am not convinced that such low level formats fit your functional/business needs. You did not say enough on your requirements for giving a definite answer (which I would probably not be able to give anyway, I haven't work in this area for about 15 years and I don't remember enough about these things).
