basement_crossfade is a very simple mac plugin designed for use in Ableton Live.
It accepts two audio inputs, and a single crossfade control determines the mix sent to its output.
You can download the plugin here:
bitbutter.com/public/basement_crossfade.vst.zip
To run this plugin you'll need to install the free max/msp runtime environment:
macmusic.org/software/view.php/lang/en/id/3140/
If you want to use this plugin in your own creations you can download the max/msp source document for this plugin here:
bitbutter.com/public/basement_crossfade.vst.zip