TheoryPDA

TheoryPDA was a line of personal digital assistants designed and marketed by Theorysonic. Their main operating system is PTSUG, and the first generation model was released on 1991.

History and availability
Development of what was to become the TheoryPDA began in 1987.

Decline
Sales of TheoryPDA begin to decline in 1997, after the success of TheoryPhone.

Software
The TheoryPDA runs Portosic OS from 1997 onwards, previously used TS-UGOS for TheoryPDA from 1991 to 1997.

Reception
The TheoryPDA has received positive reviews.