The majority of rusEFI code is written in very plain C++ ("C with classes"), with rusEFI console and some code generating tools written in java.
Most of the needs are within the C/C++ firmware and automated testing.
A good first contribution could be adding some automated testing into https://github.com/rusefi/rusefi/tree/master/unit_tests/tests
For current coverage report see https://rusefi.com/docs/unit_tests_coverage/
Doxygen source code documentation is found here.
Our primary tool-chain is GCC+Eclipse but we also support IAR.
Testing coverage open tickets: https://github.com/rusefi/rusefi/labels/automated_testing
All open tickets: https://github.com/rusefi/rusefi/issues
See Try It for how to work on rusEFI code with zero or minimal hardware.