AU Lab is a free audio suite that's part of Apple's Xcode package. It
allows to works to several Audio Units and it's particularly handy as
a fast way to host Virtual Instruments, especially if you're on a low
end Mac or if you need a portable solution for your setup.

Moreover, it's very easy to set it up to run 32-bit plugins on newer
versions of OS X, versions on which it can be difficult to find an
appropriate build of GarageBand or Logic to do so.

 * DL #1: AU Lab 1.0.3 from Xcode 2.5 (Tiger). PPC/Intel x86.
 * DL #2: AU Lab 2.2 from Xcode for Snow Leopard. Intel x86/64.

Compatibility
Architecture: PPC x86 (Intel:Mac)

DL#2: Tested on Mac OS X 10.6 Snow Leopard and 10.11 El Capitan,
possibly runs on older systems.