Avr-rfm12 is a project mainly written in C, it's free.
This project aims to provide an opensource alternative DIY source for home automation. This project use some opensource software and hardware.
PCB ===
Software:
To install the component in your gschem installation dir : $ sudo cp gschem-components/* /usr/share/gEDA/sym/local/
The first PCB is a Atmega32u2 (or AT90USB162) that connect to USB and send/receive infos thought the RFM12.