Airwindows has released Average, a free lowpass filter plug-in for Mac OS X and Windows in AU and VST effect plug-in formats.
This plugin is a straight-up extremely simple averaging filter. If you set it to integer values, it exactly averages that number of taps on the input audio (adjacent samples). If you pick in-between values it interpolates, causing the 'frequency' of the filter to smoothly blend between the values.
