Freeware - AXP CharBooster VST Plugin

https://www.kvraudio.com/product/charbooster-by-axp

CharBooster is a composite overdrive effect tailored specifically to be used as booster in front of any virtual amplifier model. It essentially consists of a pre-emphasis filter section designed to provide a variation of voicings for your instrument followed by a saturation circuit that excites the signal with harmonics while still being as transparent as possible. The UI is not trying to look like a hardware stomp box but rather has a range of meters and scopes to provide an insight on what is going on with your signal.