|Abstract:||The UMass Moo is a passively powered computational RFID that harvests RFID reader energy from the UHF band, communicates with an RFID reader, and processes data from its onboard sensors. Its function can be extended via its general-purpose I/Os, serial buses, and 12-bit ADC/DAC ports. Based on the Intel DL WISP (revision 4.1), the Moo provides an RFID-scale, reprogrammable, batteryless sensing platform. This report compares the Moo to its ancestors, documents our design decisions, and details the Moo's compatibility with other devices. It is meant to be a companion document for the open-source release of code and specications for the Moo (revision 1.0). We plan to make an initial batch of Moo 1.1 hardware available to other researchers in June 2011.