Respiratory motion continues to present challenges in the delivery of radiation therapy to tumors in the thorax and abdomen by causing movement of structures within those areas. Several approaches to account for this movement in the planning and delivery of treatment have been developed over the past several years. To assist in the development and assessment of various techniques for respiration-correlated radiation therapy, a platform capable of programmable irregular longitudinal motion has been designed and fabricated to simulate intrafractional respiratory motion. A sliding platform and the base on which it was mounted were constructed from polycarbonate plastic, and a stepper motor provided platform motion. Respiratory motion data, either artificially generated on a spreadsheet or extracted from respiratory monitoring files, were converted to a format appropriate for driving the stepper motor. Various phantoms were placed on top of the platform and used in studies related to respiration-correlated radiation therapy. Several applications of the platform were demonstrated, such as improving the quality of acquisition of time-dependent computed tomography image datasets, comparing various methods of acquiring such datasets, and implementing feedback-guided breath hold treatment delivery procedures. This study showed that a platform capable of programmable irregular motion is a useful tool for the development and assessment of procedures related to the effects of respiratory motion in radiation therapy.