The problem is that the default configuration of Homebrew's gnuplot
doesn't support any terminals for displaying the plots. To add support
for x11, ...
brew uninstall gnuplot;
brew install gnuplot --with-x
I don't know if Homebrew supports qt or not. You might experiment with
that ... or ask the Homebrew help list.
Homebrew definitely doens't provide Aquaterm. But if you are up to a
bit of hacking, you'll first need to download and install Aquaterm
http://sourceforge.net/projects/aquaterm/
And then setup the Homebrew build of gnuplot to link to the Aquaterm
libs. If you need help with that, please inquire on the Homebew and/or
gnuplot help lists.
Beware of multiple installs of Aquaterm and/or gnuplot. You'll save
yourself a lot of head-aches if you only have one of each installed on
your computer.
Ben