Tim has written another oscilloscope script for the Bus Pirate.
The script (distribute under GPL) is attached, as are a couple of screenshots. The first displays the triggering function with the trigger voltage level (horizontal dashed line) and the trigger point (vertical dashed line) shown on the graph. The second shows the spectral analysis function for a 250Hz square wave input (the higher frequency peaks are harmonics). You can also save sampled data and the plots of this data to disk.
Via the forum.