Shrew is a collection of projects for small form factor wireless sensors and related work. The first (and currently only) shrew boards are Shrew-U, for the ukhasnet network.
Shrew-U have a Si1062 microcontroller, which is a combined sub-GHz radio and 8051 CPU. The Si1062 is programmed in 8051 assembler. Also onboard is a uBlox UBX-G7020 GPS chipset with TCXO, a solar MPPT battery charger, and a light and temperature sensor. It is powered from a single AA cell.
The firmware is sufficiently developed to be a low-power temperature and light level sensor which reports over the radio in the UKHASnet protocol to a router.