One Wire FileSystem
Easy access to the full capabilities of Dallas Semiconductor's 1-wire devices.
The devices are uniquely numbered, cheap, and have functions like temperature sensing, switches, voltage and current sensors, humidity and memory/encryption. The connections are easy ("1 wire") to a serial or USB adapter.
OWFS supports web access, ftp access, perl, C, python, Visual Basic, php, tcl, java, and the command line). Connections can also be separated over a network.
Support for Linux, FreeBSD, MacOSX, Windows.
Support for many embedded devices, like routers, and NAS (OpenWRT, NSLUs).
Great for home automation, weather, monitoring, and more.