In case you do not want to use a full-fledged framework for cross-platform development, take a look at C++ as an option. iOS fully supports using C++ for your application logic via Objective-C++. I don't know how well Android's support for C++ via the NDK is suited for doing your business logic in C++ rather than just some performance-critical code snippets, but in case that use case is well supported, you could give it a try.
This approach of course only makes sense if your application logic constitutes the greatest part of your project, as the user interfaces will have to be written individually for each platform.
As a matter of fact, C++ is the single most widely supported programming language (with the exception of C), and is therefore the core language of most large cross-platform applications.
