To create an .app see Mac Setup
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
brew install cmake pkg-config gtk+3 poppler librsvg adwaita-icon-theme
git clone http://github.com/xournalpp/xournalpp.git
cd xournalpp
mkdir build
cd build
cmake ..
make