A sample-accurate metronome. Two simplistic modal synthesis models are available for the click: box is a small wooden box struck with a soft wooden mallet, stick a scratchy stick hit. In addition, there’s also a very synthetic beep, and finally dirac, a very nasty single-sample pulse of 0 dB amplitude and little immediate musical use.
All click sounds are synthesised once when the plugin is loaded and then played back from memory.

source: http://quitte.de/dsp/caps.html#Click

Credit: Tim Goetze