Arbitrary shaped RIR generator
Arbitrary shapes is A LOT more difficult than rectangular rooms. You either need to do image method with visibility checking or some sort of ray, particle or cone tracing algorithm.

There are few commercial programs that do this (Ease, Odeon, Bose Modeller, etc. ) and I doubt you'll find a free one. In addition the much more complicated algorithms, these need a way to enter or import complex room geometries, and extensive data bases on material (absorption, reflection, diffusion) and source polar patterns. These are all required to get a reasonably realistic impulse response. 

Most of the simpler online programs make so many simplifying assumptions, that the results tend to be very unrealistic and not useful for many purposes.