If you want to install the stable version of psisolver run:

brew tap bvoq/bvoq
brew install psisolver

If you want to install the latest master branch add --HEAD:

brew tap bvoq/bvoq
brew install psisolver --HEAD

If you want to install psisolver with gnuplot as a dependency add --with-gnuplot:

brew tap bvoq/bvoq
brew install psisolver --with-gnuplot

Once installed, you can use it as follows:

psisolver --help
psisolver <your_psi_file.psi>
psisolver <your_psi_file.psi> --dp --cdf

To uninstall the current version use:

brew uninstall psisolver