Guitarix - Guitarix is a simple Linux Rock Guitar Amplifier for https://alternativeto.
Virtual Audio Cable - Ever wanted to record your speaker output? (loopback) This is for you.
Waves GTR - From Fender® to Marshall®, Mesa/Boogie® to Vox®, and more, Waves has captured...
JACK Audio Connection Kit - JACK Audio Connection Kit|Home
GNUitar - GNUitar is guitar effects software that allows you to use your PC as guitar processor.
Loopback by RogueAmoeba - Get all the power of a high-end studio mixing board, right inside your Mac!