Ahh, sorry, I forgot to mention above that there's a bug somewhere between Homebrew and our FreeCAD formula at the moment: dependencies aren't all installed on the first try.
You might need to run the "brew install" line twice, then you should end up with a FreeCAD.app in /usr/local (or perhaps it'll be in /usr/local/cellar/freecad/HEAD-someversion - I'm currently testing on a slow VM, will edit this when it's done).
Edit: There's something broken in the app bundle creation when it's run from within Homebrew, but I'm not in a position to sort it out just yet. In the meantime, the CompileOnMac
wiki page has instructions to use Homebrew for fetching the prerequisites (as you've done), then building from source outside Homebrew. That process will produce a FreeCAD.app application bundle in /usr/local by default.
But first! I just made a couple changes to the freecad formula, so do a "brew update" before trying again. It'll take a while to build the first time, the formula currently builds only on one core (gives better debug info, you might notice we're right in the middle of some changes