Equalizer APO is a parametric / graphic equalizer for Windows. It is implemented as an Audio Processing Object (APO) for the system effect infrastructure introduced with Windows Vista.
Features:

• virtually unlimited number of filters
• works on any number of channels
• very low latency, which makes it suited for interactive applications
• low CPU usage
• modular graphical user interface
• VST plugin support
• integrates into Voicemeeter (www.voicemeeter.com)

Equalizer APO is best used in conjunction with Room EQ Wizard (www.roomeqwizard.com ), because it can read its filter text file format.

sourceforge.net/projects/equalizerapo
Discussion
Documentation
Downloads

User Interfaces:

Peace Equalizer
EQ APO GUI
mega-switcher

Resources:

Room Equalization Tutorial