OWFS (on the relay). http://owfs.org/
1Wire devices are presented as a text file that can be read/written.
Suggested minimum adaptor support:
USB9097 http://owfs.org/index.php?page=usb-usb9097 (cheap adaptor from China, requires CH341 USB->serial support & OWFS installed)
DS9490 http://owfs.org/index.php?page=usb-ds9490r (kernel module DS9490R should be unloaded to avoid conflict with OWFS)
This would allow access to existing 1Wire based home automation setups (primarily DS18B20 temperature sensors, and DS2408 8 pin GPIO). For example, I am currently implementing temperature monitoring (~50 sensors) throughout my home, as well as roller shutter control using DS2408 GPIO.