C++.

We use it for cross platform logic sharing. It adds overhead but it remains completely in your control (no third party dependencies, webviews). Performance is excellent but it adds overhead to development and expertise is required. However it has saved us so many times, I would hazard a guess that 75% of our code is shared across platforms. Devs need to know at least 2 languages (Java & C++, Objective C & C++ etc.)