Palm OS

Palm OS, created in 1996 and alternatively known as Garnet OS, is an operating system of the PalmPilot series of handheld computers with a stylus. 6 and the last update was released in 2004.

The initial version of Palm OS included:

The address book;
Diary;
Notepad;
To-do list;
Calculator.
And here are the features added to various OS updates:

Infrared port;
Color display;
Bluetooth;
Wi-Fi.
Pros and Cons
Simple interface; Old software is not compatible with new versions.
Stability of operation;     
Virus protection