Armando Mortanez has released SimpleSide, a free volume automation
plugin for Windows and Mac. SimpleSide is mainly a side chain tool
designed for simulating the pumping effect of side-chain compression. The
plugin is easy to use and only has two control parameters, a timing knob
which can be set to 1/32 and 16/1 and an automation curve editor which
allows you to add control points to shape the volume automation curve.