From the ADA:
ADA Oral Pathologist is a chair-side reference to oral pathology conditions that can assist dentists with formulating diagnoses…Conditions can be searched by name or by entering clinical observations. ADA Oral Pathologist is a reference you can use every day with photos and descriptions of the most common oral pathology conditions seen in your patients.
This is an app for both Android and iPhone for $59.99. It walks you through a step by step differential diagnosis as shown below..