AsyncHttpd is written in Java using NIO and Kilim microthreads.
Log4j with some patches to support Groovy file and line numbers in logs. More details at log4j-groovy
Simple & stupid music player plugin for Eclipse. More details at Orfeus page. Written just for fun in one evening.
EasyPage is small content management system for PHP3 written around 2000. Was used for this pages before DokuWiki.
Virtual language for internet called Netština. An satire for Czech language purism.