Theodor Groeneboom:
Sprut is a simple set of free tools for 2d fluid simulation work within The Foundry’s Nuke. Based on and around Jos Stam’s 1999 Siggraph paper “Stable Fluids”, it was created using standard Nuke 2D nodes , making it the first truly open, flexible and portable fluid toolkit within Nuke
Oh, well then.
Update:
Here is a disscussion on the nuke user fourm