How to get the latest source code

The best way would be to export or checkout from svn, depending on what you want to do with it.
If you just want to download the latest code and run it, then use export.
If you want to download the source with the intention of developing it, use checkout.

The location of the development code for FahMon is http://svn.fahmon.net/trunk
Therefore when using an svn client (like the svn command on Linux), you simply do:
svn export http://svn.fahmon.net/trunk fahmon
svn checkout http://svn.fahmon.net/trunk fahmon

Each release can also be checked out (or exported) by looking in the tags directory of the svn repository.
The folders are laid out so that each release has it's own folder.
Version 2.3.0 can be found in tags/2.3.0 for example.

Please note that the pre-built packages are not present in the svn repository, they can be obtained from the download page.