The AMXD extension is given to files that are used by a professional DAW software to create music productions called Ableton Live. AMXD files are used to store add-ons to the program, which, once installed, allow you to expand the sound possibilities with new effects, sounds or instruments. These files are created with a tool called Ableton Max for Live, which runs as a standalone application but is also included in the Ableton Suite.

Ableton is a tool developed for Windows and Mac OS X operating systems.