Xamarin Studio is not available for Linux but there are plenty of alternatives that runs on Linux with similar functionality. The best Linux alternative is Eclipse, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 100 alternatives to Xamarin Studio and many of them are available for Linux so hopefully you can find a suitable replacement. Other interesting Linux alternatives to Xamarin Studio are PyCharm (Freemium, Open Source), Apache NetBeans (Free, Open Source), Code::Blocks (Free, Open Source) and Qt Creator (Free, Open Source).
Ultimate++, also called U++, is a C++ cross-platform rapid application development framework focused on programmers productivity. It includes a set of libraries (GUI, SQL, etc..), and an integrated development environment.