This is a very small SPI connected Ethernet TCP/IP module using the WIZnet W5100 chip. W5100 is a hardwired TCP/IP processor.
It required a small fix to make the board work. The bug was about the connection of the transformer center tap.
This module works with Arduino. It is compatible with the Arduino Ethernet library in the Arduino 0012 distribution. It operates on 3.3V. However, it can be connected directly with 5V system like Arduino.