Judging from the output of brew —env, there is a MACOSX_DEPLOYMENT_TARGET you should be able to set/override. Simplest way would be when running brew:

    MACOSX_DEPLOYMENT_TARGET=10.6 brew …

That, in combination with —build-from-source when installing packages, might give you want you need.

--------
Dan Wilcox
@danomatika
danomatika.com
robotcowboy.com

On Oct 10, 2016, at 9:30 AM, Jonathan Wilkes <jancsika@yahoo.com> wrote:

> The closest might be -universal which asks to build/install a universal 32/64 bit package. There might be something else, but you’ll need to check the docs: http://brew.sh



Nothing pops out at me.  It would be an enormous benefit over Macports-- which doesn't officially support targeting versions earlier than the one you happen 
to be building against.  I assume they'd advertise that front and center.

-Jonathan