Hundreds of PID design methods are available in literature. Many of them are very similar and sometimes it is not straightforward to understand their purposes. This interactive software tool to help in the study and understanding of several well-known PID tuning rules. Frequency- and time-domain responses are analyzed in order to show the robustness and performance properties of each method. Furthermore, a free tuning option is available to provide comparisons with user-defined rules or other existing tuning methods. A wide range of process models are included in the tool, where model-reduction techniques are applied for high-order processes to obtain simple models for design purposes.