Not free, but this is my favorite:
http://www.ikmultimedia.com/t-racks/moreinfo/moreinfo6.phpHigh precision, high definition Linear Phase Equalizer
What it is
The T-RackS 3 Linear Phase equalizer is a precision tool that allows for extremely detailed, clean and transparent tonal changes intervention on your audio material.
This equalizer is used for working on the tonal balance of the audio program with no additional color added providing total transparency and respect of the original sound. Linear Phase Equalization is a process that is only possible in the digital domain.
What it has
The T-RackS 3 Linear Phase EQ is comprised of six bands of fully parametric equalization, each band can be configured to work as a high pass, low shelving, peaking, high shelving or low pass, thus making the module extremely flexible.
Why You need one
This equalizer is perfect when you need to make eq adjustments on the audio program and have it not “appear” as equalized — This Linear Phase EQ allows you to make adjustments that sound as natural as possible, as if the audio was never touched.
When used in Linear Phase mode, no time and phase shifts are applied to the audio at the points where the program has been filtered. This allows for applying tonal enhancements as needed, but doesn’t add “colouring” to the sound, leaving it pristine and completely natural sounding unlike the operation of a conventional equalizer.
Linear phase equalization also allows for extremely delicate and critical operations on audio recordings, for example it will be possible to equalize your samples without creating clicks on the loop points, it will be possible to mix the original sound and the equalized one without having any phasing effect.
Also, if you recorded an instrument with multiple microphones, it will be very hard to maintain timing alignment by applying different equalizations to each microphone. Using Linear Phase equalization, instead, will make the EQ process to only apply tonal changes without any timing and mic-to-mic phase relationship alteration.
In critical mastering applications the T-RackS Linear Phase equalizer is the perfect choice when you want to either apply broad, gentle and crystal transparent tonal shaping or when you need to precisely intervene on a very narrow frequency spot in the most natural and undamaging possible way.
Listening to the musical program while toggling between the Linear or Minimum Phase modes clearly shows off the difference that a traditional phase-shifting analog-style EQ and a the Linear Phase process makes on music, Traditional EQs apply phase shift and thus “color” your sound inducing the character of the eq unit into the sound. The application of the Linear Phase EQ is less intrusive, less coloring and more respectful of the original tone and balance of the music.
All module processors and metering are also available as individual plug-ins for more convenient mixing within your DAW.