Inter-Thread Communication (ITC) aims to make it exceedingly easy to call functions in other threads. The lexer does all the work, so just run the lexer on your headers, then call the stub functions. In addition, it also provides a complete threading API, with the four threading primitives and a high speed threadsafe FIFO class.
Faith is a cross-platform C++ graphical application toolkit. It runs natively on Linux/Unix (Xlib) and Windows. It has an API strongly inspired by Qt's and has many features that are expected from a modern toolkit, including a variety of common "widgets", an aesthetically pleasing appearance, and the many critical non-portable components such as anti-aliasing and sockets.