Touch and stylus sensitive computer displays are widely available. Yet, the development of gesture sets to support these interaction methods continues to be difficult. We present RATA, a tool for interaction designers and software developers to create gesture recognizers for novel and custom gesture sets. Guided by the RATA wizard, the developer: defines their gesture set; collects example gestures; labels them with the support of an auto labeller; and generates the recognizer model file -- no coding or expert knowledge of recognizers is required. Incorporating the recognizer into a program requires just two lines of code. Our evaluations show high user satisfaction and that novice software developers can design a customized gesture set and generate a recognizer in about 20 minutes.