Pendulum - Pen Pal Tracker is a free utility tool available for iPhone users. The program, developed by Benjamin Cardy, allows users to keep track of their pen pals effectively. Users can add friends, log when letters are sent or received, and track the delivery duration of their correspondence. Additionally, users can document the pen, ink, and paper used for each letter to maintain variety in their writing.

With built-in reminders, users are prompted to respond to pen pal letters in a timely manner and avoid forgetting about drafted letters. The program offers iCloud synchronization, enabling users to stay updated across multiple devices seamlessly.