Forum thread. Here you'll find links, screenshots, a Youtube video, the changelog, and sourcecode links. Go there to report bugs, make feature requests, and give feedback (which is, by the way, always welcome).
When targeting a docking port, your navball gets an additional red marker that shows the orientation and roll of your target. Just point towards that marker, and you'll be perfectly set up for docking; once you're oriented, the rest of the docking can be done using translation controls only.
Typically, this plugin allows you to dock by looking at nothing but the navball, never switching vessels, and saving tremendous amounts of RCS fuel.
The mod is designed to be minimalistic; all it does is add that red marker. It therefore has almost zero memory/framerate impact and hasn't caused a single crash (that I know of). It is also part-free, i.e. it will automatically work with all vessels.
The marker color and texture can be changed via config file (recommended for colorblind people); see the readme file for details.
For a long time, I knew that docking needed just something to make it less annoying; some kind of additional rendered line on screen, but I never really knew what precisely it was - until I discovered NavyFish's awesome Docking Port Alignment Indicator mod. It gave me the whole idea for this mod, and I wish to thank him for that. However, the plugin had too many features for my taste; it opened an additional window, and displayed a lot of redundant information that is already in the navball. By that time, kitoban had already written his equally awesome Enhanced Navball mod, so I had everything I needed: The idea, and example code that shows how to draw markers to the navball; I wish to thank kitoban for his pioneering work in that field. In v3, taniwha added code to allow for more targets than just docking ports; this improves compatibility with his Extraplanetary Launchpads mod.