Ferret 4x4 is a free 32/64-bit VST plug-in for Windows and a 32/64-bit VST and AU plug-in for Mac OSX.
It has been primarly designed to enhance the routing capabilitiels of eaReckon BloXpander (but it works with other compatible host software).
This plugin makes use of BloXPander's specific "sidechain" and multiple outputs capabilities allowing complex audio routing.
You can assign outputs pairs of other plugins to 3 of the 4 Ferret 4x4 inputs (Ferret 4x4 is "sidechain" capable).
You can then link 3 of its ouputs to 3 different channels (Ferret 4x4 has multiple outputs pairs).
"Input 1" and "Output 1" are direct links.
The 4 inputs are processed and down-mixed before they are sent to the 4 outputs.
Freeware by EaReckon