CIS DSP Factory has released Betty Middle a free bass centering plug-ins. Betty Middle uses m/s techniques to control the stereo width of the audio signal. It can be used as a stereo enhancer (capable of widening the image up to 200%), but it is also capable of centering the bass frequencies in a mix.
Betty Middle features:
Betty Middle is available for free as VST plug-in for Windows at CIS DSP Factory.