ZNC doesn't use SVN anymore, it now uses Git instead.
What is SVN?
Subversion is an open source application for revision control. Also commonly referred to as svn or SVN. It is used to maintain current and historical versions of files such as source code, web pages, and documentation. Its goal is to be a mostly-compatible successor to the widely used Concurrent Versions System (CVS).
Is the ZNC code in SVN the bleeding edge? How stable is it?
It's definitely cutting edge. Bugfixes will show up in SVN very early. New features, however, won't show up in SVN before they have somewhat stabilized. This means that SVN versions usually are very stable, but may still contain unknown bugs. If you'd like to help make ZNC better, you are invited to check out the latest revision from SVN and give it a whirl.
How do I get the latest SVN revision?
There basically are two ways. One way is to use the svn client utility from your command line:
Without subversion you can use http://znc.in/nightly/znc-latest.tar.gz to get a tarball of the trunk. A new nightly tarball is generated every night, so if there has been a fresh update to SVN, it will usually take some hours before the nightly has the update as well.
Alternatively, you can try to get a tarball from Sourceforge: http://znc.svn.sourceforge.net/viewvc/znc/trunk.tar.gz?view=tar
Where do experimental patches etc. go?
SVN Repository Structure
branches on svn.kuja.in: contains the development branches of the users working there, currently it's only crox
tags: empty as of now
trunk: the main directory for development is here, though don't use the trunk on svn.kuja.in, it's broken
To see the latest changes in the SVN repository structure check here: http://znc.svn.sourceforge.net/viewvc/znc/
What is the crox repository/branch?
The SVN repository on Sourceforge is the primary repository, the code in that repository will definitely find its way into a new release.
The SVN repository on svn.kuja.in has been used for development work that didn't find its way into the Sourceforge one mostly because either the stuff there needs to be tested, isn't considered ready for merging by the developers or is made by non-ZNC developers and isn't merged into mainline yet. It's very outdated, currently! If you want to have a look anyway:
svn co svn://svn.kuja.in/znc/branches/crox znc