From Dirk's Projects:
Tune a piano yourself to a professional standard. It's surprisingly easy with this software. Many instruments can be tuned using a simple tuning device. Each tone is then tuned exactly to a predefined frequency. This method can't be used tuning a piano. Dirk's Piano Tuner analyzes your instrument and uses the results to calculate the optimal tuning for your piano in particular. Using this calculated setting, you can then tune your piano, in no time, to a professional level, without having to go through the classical, time consuming, process of 'checking the intervals'.