Odo Synths has released c64it, a small effect plug-in that can be used to transform audio to sound like the C64.
The c64it plug-in features a simple interface with 3 knobs: Pregain, Crush and Level. The Pregain is useful when the plug-in is fed a low volume audio input. The Crush control sets the amount of bit crush and level controls the output volume.
There’s no information on Odo’s website yet so get the latest version of c64it here.