monoLOW is a "low band conformance machine". monoLOW is just about the simplest tool going. The lower its frequency, the more a sound loses its directionality. It sometimes makes little sense for frequencies below a certain point to be spread across a stereo mix - a stereo bottom-end can cause a loss of focus. Enter monoLOW.
2 simple controls allow mono-izing of the low band: "frequency" below which all is mono, and a "cut / gain" control for level. Audition and defeat buttons are also present.
A free version that stops working for 5 seconds every 5 minutes is also available (the full version doesn't do this, obviously).