A new automated Monte Carlo software for clinical linacs and dose distribution simulation, named PRIMO, has been recently released.
Its computation engine is based on the well-known PENELOPE code.
PRIMO can simulate most Varian and Elekta machines, as well as imported phase-space files written in the IAEA format, and estimate dose distributions in water phantoms and computerised tomographies.
All these features are wrapped under an intuitive graphical user interface that runs on Windows.
The code can be freely downloaded from http://www.primoproject.net.