Juno Ju-X has released Hosting AU, a "microDAW" for Mac OS X that hosts Audio Unit synth and effect plug-ins.
It comes with a 4ch+1 mixer with ext-audio input, 24-bit recorder, a "Music-Typing" kind of feature called "LazyKey".
Backward compatibility is up to 32-bit Carbon-based plug-ins no matter on Snow Leopard to the latest Mavericks. So most older plug-ins will run.
Visit www.ju-x.com for more information. It's a free download without any limitation.
