Probably the most popular of my free code offerings at the moment is "Friki", my Java Wiki. A Wiki is an editable web site, where visitors can freely add, edit and link pages just using a web browser, and without knowing the complexities of FTP, HTML or whatever.. A strange concept, but very useful.
I currently manage development of this project at Sourceforge, and you can download both a drop-in "war" file and the documentation and source code from there. Friki is currently at release 2.0.6. It's stable, has been downloaded hundreds of times, and in use by several major web sites, including the frequently asked questions (FAQ) at The Java Ranch. If you want to try using Friki, I have a demo installation running at http://tomcat.efsol.com/friki/. Have Fun!