AD5241 and AD5242 provide a single-/dual-channel, 256-position, digitally controlled variable resistor (VR) device. They have 2-Wire I2C Compatible Digital Interface.
Digital Potentiometer - AD5242 - Analog Devices
They are Analog Semiconductor Replacements for Electromechanical Devices like potentiometer, trimmer or variable resistor.
The Advantage of the latter is low cost and easy to configure and use. The Advantage of the Digital Version is "No moving Parts". hence not limited to things like "10000 operations". Another clear advantage is precision and vibration resistant.
See an Application of this Digipot in a TinyOS hardware magnetometer..
The temperature stability of 30 ppm/°C and low noise settings is also achieved with SiCr thin film resistor technology. They range from 10K, 100K and 1M Ω End-to-End Terminal Resistances.
Digipots are not for high currents or power, even high voltage and very low resistance values are not for these devices. These are signal control devices. Use it for analog circuits and instrumentation and signal control too.