Silverback is a guerrilla usability-testing app for people who design and build websites.
With Silverback, you can run your own low-cost, unobtrusive usability tests using the hardware you already have in your Mac. Silverback records screen activity and iSight video, along with audio and mouse clicks. Once your test is finished, all Silverback video and data is compiled and exported as a Quicktime video.
Silverback 2--available through the secondary download link above--is now available as a free but unsupported product in order to support older machines and operating systems (OS X 10.4-10.9).
Updated on Jul 10 2015
Note: Silverback is available for $39.99 until 12 July 2015.
Note: Now requires OS X 10.10 or later running on a 64-bit Intel processor.