Nimrod/O: A tool for automatic design optimisation using parallel and distributed systems. Nimrod/O (part of the Nimrod toolkit) allows a user to run an arbitrary computational model as the core of a non-linear optimization process. Nimrod/O allows a user to specify the domain and type of parameters to the model, and also a specification of which output variable is to be minimized or maximized. Accordingly, a user can formulate a question like: what parameter settings will minimize the model output?. Nimrod/O currently employs a number of built-in optimization algorithms, namely BFGS, Simplex, Divide and Conquer and Simulated Annealing. Jobs can be executed on a variety of platforms, including distributed clusters and Computational Grid resources. Nimrod/O has been used for a range of design projects including the optimal design of aerofoils, highly durable mechanical parts and high gain antennas