Its still in a very early stage, but more than usable by now.

Release notes by alex (thanks!)

Known bugs:

 * it's easily fooled by contrast (or lack of it)

 * it may display red markers even if there's nothing in focus

Implementation details:

 * Only horizontal edges are detected.

 * Only adjacent pixels which fit in an int32 are considered.

 * Threshold: 1% percentile.

 * When recording, HD buffer is downsampled horizontally by 2.

Update:

• Fixed the saving bug (you can now save the Focus Peak setting).
  
• Added some kind of color coding (warmer is better)
  
• Small optimizations (I'm not sure if they have any effect or not).
  

Try it out here:

http://groups.google.com/group/ml-devel/browse_thread/thread/d29edd39ae8db9ae/5d0f4b966faf86aa?show_docid=5d0f4b966faf86aa

or here