Hbasm has released a freeware mono compatible Stereoizer VST plugin made with Synthmaker.
The stereoizer is modelled it after an old hardware-synth. It works by adding a phase-inverted, slightly delayed, discrete chorus to the dry signal. Unlike a typical chorus effect, which tends to turn a solo-instrument into an ensemble sound, this stereoizer is more transparant. Its also not a typical “delay” effect, or a “surrounder” which isn’t really mono-compatible.
Stereoizer is mono-compatible: If you monoize the sound again (left channel + right channel) the effect will disappear completely, leaving only the original sound. This has the benefit that you can use it on basses, even kick-drums, as well as any other sound. People who listen to your music in mono will not hear the stereoizer at all. Stereoized basses won’t sound sloppy on sound-systems where there are only one loudspeaker (sub-woofer) for the bass.
You can download Stereoizer here.