The uWatch is an RPN and Algebraic scientific calculator watch that you can build yourself.
The software is OPEN SOURCE under the GPL license.

Specifications:

• Processor - 16 bit Microchip PIC24FJ64GA004

• Program memory - 64KB of Flash

• SRAM - 8KB

• Available user EEPROM memory - 64KB

• Calculator modes - 4 Level HP style RPN stack, or Casio (pre-VPAM) style Algebraic with 6 level of parentheses

• Latest firmware support complex number calculations, moon phase display, and plays games like CHESS and 21.

• Precision - 64bit IEEE floating point. 9 digit display + exponent

• Programming - Macro style keystroke programming mode. 60 x 1024 steps.

• Time and date display. Selectable 12/24hr format

• Clock Speed - 250KHz normal operation, 32.768KHz sleep mode. 8MHz maximum speed.

• Display - 16 character x 2 line dot matrix

• Sleep mode - LCD switches of after timeout to increase battery life. Picks up where it left off.

• Backlight - Yellow LED (quite dim)

• Battery - single or dual lithium CR2032

• Battery life - 100hrs+ operation. 1 year+ in sleep mode.

• Size - 54mm x 43mm x 20mm(at the thickest point)

• Watch band - any standard 20-22mm watch band. Standard 22mm watch spring bars.

• Programming Interface - Microchip ICSP. Compatible with MPLAB ICD2 or compatible programmer.

• Serial port - UART based universal serial port. RS232 and IrDA compatible with optional interface circuits.

• Language - All source code written with the free MPLAB C30 compiler

 

Here are some very early promotional videos of the first prototype (WMV format):

• uWatch Introduction

• uWatch Modes and Menus

• uWatch Algebraic Mode Operation

• uWatch Keystroke Programming