Parslet makes developing complex parsers easy. It does so by

* providing the best error reporting possible
* not generating reams of code for you to debug

Parslet takes the long way around to make your job easier. It allows for
incremental language construction. Often, you start out small, implementing
the atoms of your language first; _parslet_ takes pride in making this
possible.

Homepage:
http://kschiess.github.com/parslet/
