jEdit is an open source text editor written in Java, offering a great flexibility for programming through it's very good plugin architecture.
The jEdit plugin is the first implementation of DocSynch. It is also considered as the "reference" implementation.
There is a docsynch-jedit package at the file release site of the sourceforge project, where you can download the latest available version.
Not a true nightly build, but a fresh development version (21.10.2004 - 11:27).
See the release notes of the file release you downloaded (click on the bold version number with a book icon in front of it). The same text is also included as README.txt inside the downloaded archive.
Appropriate IRC client
jEdit IRC plugins starting from version 2.0 and upwards work with the DocSynch plugin. Look here for more information about the IRC plugin.