There are a few drawbacks to this ENC28J60 Ethernet shield – the official Arduino Ethernet shield has a 10/100 Mbps connection where the Microchip-powered shield is limited to 10 Mbps.

Electronica: Arduino makes single-pair Ethernet accessible, and RS485 too Arduino announced a single-pair Ethernet adapter board for its Uno R4 single-board microcontroller at Electronica this morning ...

Arduino have taken the tiny wraps off of the official ethernet shield for their open-source prototyping platform, which adds network connectivity to the device. Based… ...

An UNO Shield that stacks onto Arduino boards (or Arduino-like boards such as Mbed) and provides an SPI interface to data packets that are sent or received using the EtherCAT protocol.

The problem with using it along with Arduino-based gadgets is that you then need to use something like an Ethernet shield to provide the network connection.

OMC's H19 fiber-optic shield has been adapted as a stackable add-on for the Arduino Uno. It’s designed to simplify the integration of fiber-optic data links into microprocessor-based platforms.