The Arduino Ethernet is a microcontroller board based on the ATmega328. It has 14 digital input/output pins, 6 analog inputs, a 16MHz crystal oscillator, a RJ45 connection, a power jack, an ICSP header, and a reset button.
An optional Power over Ethernet module can be added to the board as well.
The Ethernet differs from other boards in that it does not have an onboard USB-to-serial driver chip, but has a Wiznet W5100 ethernet chip. This is the same interface found on the Ethernet shield.