Some weeks ago, GNS3 released its beta version, here is the way to install it from scratch on ubuntu/elementaryos :
1/ You need python 3.3 or higher, pip, qtmake and other stuff :
~ sudo add-apt-repository ppa:fkrull/deadsnakes
~ sudo aptitude update
~ sudo aptitude install git python3.4 python3.4-dev qt4-qmake ...