The GNOME software center doesn't allow you to install all available programs.
Install Synaptic to manage all installable programs and gdebi to install tird party .deb instalation files.
sudo apt-get install synaptic gdebi
managing ppa's using Y-ppa manager
sudo add-apt-repository ppa:webupd8team/y-ppa-manager
sudo apt-get update
sudo apt-get install y-ppa-manager