Edyuk is a free, open source, fast and lightweight development environment which supports C++ and Qt 4 out of the box and can be extended through plugins. It works under all platforms supported by Qt 4 (Linux, Mac, Windows, BSD, ...).
A Finite State Machine Editor, written on QT. It allows to draw Finite State Machine with easy GUI and store it in XML file. There are Finite State Machine Compilers to translate this description to source code (technique like QT's UIC uses).