FreeAMP - Audio Gear Modeler

Nice, simple, but quite good sounding and working analog / tube saturator.

More American than British voiced in my opinion. I mostly use it with guitar, there you get some nice "Fenderish" tones with some good, sparkling, transparent treble and also some nice vintage overdrive.

In case you look for a "hotter" sound, stacking two instances also works well and can sound good.

Just add a good cabinet IR and you get some comparably transparent, but not digital sounding (tube amp) tones.