Shrimp is a free visual renderman shader creation tool for linux
Shrimp shaders are made of a circuit of blocks or functional units that all take a number of inputs and return a number of outputs. The function might be quite simple, like multiply the inputs together, or more complex, such as displace the surface a specified amount along a specified vector.
A SHADeR, then, can be built by connecting together the inputs and outputs of different blocks. Once this is done, Shrimp will write the neccessary shader code and can call the compiler and renderer to preview it. The generated code should work with any Renderman compliant renderer such as BMRT or Aqsis.

Shrimp is still in development, but it can still be used to Create shaders. The current task is to extend the range of Building Blocks neccessary to create all kinds of shaders. This is on going work, but if you would like to contribute any blocks youve written send them to me.
The User Interface is all specified in a number of xml files. This means that new blocks can be added without recompiling Shrimp. you can free download Shrimp 0.4.1 now.