From the webpage:
Stan is an open-source package for obtaining Bayesian inference using the No-U-Turn sampler, a variant of Hamiltonian Monte Carlo.
I first reported on a presentation: Stan: A (Bayesian) Directed Graphical Model Compiler last January when Stan was unreleased.
Following a link from Christophe Lalanne’s A bag of tweets / September 2012, I find the released version of the software!
Very cool!