Naiad
http://www.exoticmatter.com/overview/ I've recently been made aware of this new product called Naiad. It is for the most part a solver for dynamic bodies such as fluids and gas. It is also an open source software package that is part of a standard which other software can also be written to conform and process data from the Naiad Graph. This is a full GUI front-end for the artist to interact with the solver. Although it is relatively new to the scene, it has already been used for solving gas and fluids in quite a few feature films, including Avatar, Harry Potter and the Deathly Hallows Part 2, Pirates of the Carribean 4, Narnia: Voyage of the Dawn Treader, X-men: First Class, The A Team, Final Destination 5, etc. Although Naiad is now only available on the Linux platform, versions for Windows 7 and Mac OS X will be announced later in the year. Go to the movies page to see examples of the solver in use.