Emacs Freex mode is a minor mode for organizing and editing a massively-hyperlinked database of your notes and ideas. It's a personal wiki on steroids.
For a more detailed description, read the Introduction.
You can grab the latest version from the Downloads page - freex-x.x.x.tar.gz.
Make sure to read the Installation instructions though.
If you learn best by seeing, watch the intro screencast.
If you learn best by doing, then you might want to skip to the Quickstart or Tutorial, and try working through things yourself.
The Freex codebase has been pretty stable since about 2007, though we continue to make minor tweaks to improve the interface and make it easier to install. We made a clean break with the old Mercurial revision history when we switched to hosting with Google Code in 2009.