Red Bass (free version) by UnplugRed

sub oscillator sidechained to incoming signal.
put a drum loop or a kick thats lacking some oompth in there and the result will be instantly thick.
apply with caution if not in a proper mixing environment.

Available for both windows and linux, in VST and VST3 formats, 64-bit only.
More info: https://vst.unplug.red/