The name Motega stands for 'Modeling Of Tubes Employing Genetic Algorithms'. Motega is software, written in Matlab, that generates pSpice tube models from datasheet data. A genetic algorithm is used in order to find optimal values of all parameters in the tube model, giving the smallest possible error between the tube model and the actual tube itself.
On two separate pages, see the menu at the left, an overview of the Motega software is provided:
A zip-file containing the Motega software can be downloaded from my 'Software' page. That page also gives a brief explanation of the Matlab programming environment.