- Clean separation of the "framework" from the processing stages, including generalization of the tricky business of configuring compiler flags
- Pragmas for setting header search paths, trigraphs, whitespace preservation (including emitting #line directives), and including headers "once"
- Very nice error messages, tracing macro expansions like Clang does, but better
- Header guard optimization and a fast string class, now only ~2.5x slower than GCC
- Numerous small fixes and tweaks
The source is still available at Google Code.