Phillip van Eeden developed a C-like language for the NXT, along with an IDE, called nxtC.

I only had a brief chance to try it, but here is Phillip’s list of the main features of nxtC:

• Functions can be multilevel. There can be functions in functions (like Delphi).
• Library of functions that only compile functions that are used. The library can be pre-compiled and encrypted.
• Classes with inheritance. Classes can be multilevel (classes in classes).
• NBC assembler functions can be directly used in a function.
• Fantom driver functions are integrated in the IDE and can be programmed from the PC.
• Bluetooth implementation for downloading and communication with the brick.
• More than 10 program flow structures and programming syntax enhancements.
• The compiler translates nxtC programs (text files) into NBC files (*.nbc) - to be compiler by nbc.exe