Matthias Kock has released Tilt EQ, a free tilt equalizer plugin that offers a linear tilt function with a single knob, offering an easy way to change the spectral balance of audio material without introducing coloration.
Tilt EQ is based on FIR filters that can be either linear or minimum phase. Baxandall minimum phase IIR filters also have been implemented in order to allow further adjustments.
Tilt EQ is a free download for Windows and Mac (VST/AU). Donations are welcome.