Palm and Palm OS devices are the most widely used pen-based kind of Personal Digital Assistants (PDAs). The original series of Palm Pilots (models 1000, 5000, Personal, and Professional) were made by USRobotics, which was bought by 3Com. Since then, the unit has spun off and is now Palm Computing, Inc. Palm has about a dozen different models on the market. Palm OS, the operating system running on Palms, has been licensed by other manufacturers, and some OEMs sell branded versions of Palms. Thus, Palms are compatible with Handspring's Visor, Kyocera's pdQ cellphone, the Symbol Technologies SPT series, and TRG Products. Other licensees include Sony and Nokia. The IBM WorkPad and the ePocrates are branded Palm models.