I have run it only after installing some dependencies. ("sudo apt install python-pip", "pip install --upgrade pip", "sudo pip install -U setuptools", "sudo apt install graphviz libpython-dev python-dev libxml2-dev libxslt-dev"), then run /tmp/w3af_dependency_install.sh and only then I have succesfully runned "python /home/username/w3af/w3af_gui".
Unable to install on Mint 16 Cinnamon. Keeps asking for python2.6-dev and my system has 2.7-dev. Unable to run it