SelWX is a project mainly written in PYTHON and C, it's free.
A weather station
SelWX
A weather station in Selwyn College, Cambridge, UK.
Reads weather data from a wind vane, anemometer, rain cup, light sensor, relative humidity sensor, light sensor, temperature sensor and barometric pressure sensor. Sends this data to a web application over ethernet and the internet at large.
By Jon Sowman & Adam Greig May 2010