You can also download it as jflex package for Debian or Ubuntu GNU/Linux (aptitude install jflex)
You can download it as javacc package for Debian or Ubuntu GNU/Linux (aptitude install javacc)Documentation and grammar examples inside the zip file
The above version has some changes compared to the official that you may find useful
Download it from the above link and for platforms debian/ubuntu gnu/linux download the package "spim"
Website (for POSIX systems like Linux, BSD, Unix*)