Balsamiq en Ubuntu 13

Paso 1 – Descarga Adobe Air 
wget http://airdownload.adobe.com/air/lin/download/latest/AdobeAIRInstaller.bin

Paso 2 – otorgar al archivo permisos de ejecución
chmod +x AdobeAIRInstaller.bin

Paso 3 – Ejecutar el instalador
sudo ./AdobeAIRInstaller.bin

Paso 4 – Descarga Balsamiq
wget http://builds.balsamiq.com/b/mockups-desktop/MockupsForDesktop64bit.deb

Paso 5 – Instala Balasmiq
sudo dpkg -i MockupsForDesktop64bit.deb

Posibles Errores:

Si tu sistema operativo es 64bit: "error while loading shared libraries: libgtk-x11-2.0.so.0: cannot open shared object file: No such file or directory"
sudo apt-get install ia32-libs-gtk

Gnome Keyring or KDE KWallet: Sorry, an error has occurred. Adobe AIR could not be installed. Install either Gnome Keyring or KDE KWallet before installing Adobe AIR.

Para detectar el path: locate libgnome-keyring.so
Luego ejecutar el instalador con el path: sudo LD_LIBRARY_PATH=/usr/lib/x86_64-linux-gnu ./AdobeAIRInstaller.bin

Sino, intentar con:
sudo ln -s /usr/lib/x86_64-linux-gnu/libgnome-keyring.so.0 /usr/lib/libgnome-keyring.so.0
sudo ln -s /usr/lib/x86_64-linux-gnu/libgnome-keyring.so.0.2.0 /usr/lib/libgnome-keyring.so.0.2.0



Fuente: http://www.randomhacks.co.uk/how-to-install-balsamiq-mockups-on-ubuntu-13-04/