J2ME (Java 2 Platform, Micro Edition):
J2ME, developed by Sun Microsystems Inc., provides an environment for applications running on consumer devices, such as mobile phones, PDAs, and TV set-top boxes, as well as a broad range of embedded devices.
Palm OS:
Palm OS, developed by Palm Source Inc., is a fully ARM-native, 32-bit operating system running on handheld devices.
Symbian:
Symbian Ltd. is a software licensing company that develops and supplies the advanced, open, standard operating system—Symbian OS—for data-enabled mobile phones.
Windows Mobile:
Windows Mobile is a compact operating system for mobile devices based on the Microsoft Win32 API. It is designed to be similar to desktop versions of Windows.
They apply different approaches to accomplishing handheld computing.
The figure below shows a generalized development cycle applied by them:
