The code for Friki itself (all the com.efsol.friki classes) can be found under src/delivery/java. The test code (which will be compiled and used if you have installed AntJUNIT) can be found under src/test/java. Friki does, however make use of a bunch of other classes from other projects. Any classes in the package JREGEX are from the jregex project. Any org.stringtree classes are from the StringTree project. Any JLIBDIFF classes are from the jlibdiff project. Source code for all these may be downloaded from SourceForge.
If you are interested in coding a wiki yourself see the excellent series of articles by FrankCarver at the JavaRanch.