DirectFB is a thin library that provides developers with hardware graphics acceleration, input device handling and abstraction, an integrated windowing system with support for translucent windows and multiple display layers on top of the Linux framebuffer device. It is a complete hardware abstraction layer with software fallbacks for every graphics operation that is not supported by the underlying hardware.
BlueSense SDK is a software development kit for communicating with BlueSense equipment. It allows you to read out sensors or control actuators. A user-space USB driver for all platforms is included. Examples for all modules are also included. For Java and Mono/C#, there is an object-oriented interface, and for C, there is a function based interface.
OWFS (One Wire Filesystem) allows easy control of the 1-Wire bus under Linux. The bus can either be viewed in a Web browser (OWHTTPD) or as files (OWFS). This makes manipulating the 1-wire devices easy with shell scripts, Perl, C, and other programming languages. 1-Wire devices are intriguing chips made by Dallas Semi. They are cheap, uniquely numbered, and take minimal wiring to connect (a data/power line and ground are all that's required. Chip functions include memory, switches, counters, and sensors of temperature and voltage.
X10MMS is a software suite that provides support for the X10 CM19A USB home automation transceiver under Linux. It allows users to control the device directly, sending and receiving basic on/off commands, and also includes a sample application that allows XMMS to be remotely controlled using the CM19A transceiver and an X10 palmpad remote. The current CM19A driver is implemented as a kernel module and requires an up-to-date 2.6.x kernel. The program is completely user configurable via a straightforward text file, so you can assign any supported function to any toggle key on the remote.
Device::ParallelPort is a Perl API that allows low level access to the parallel port of most computers. It does this by using a number of drivers, which can be customized and added to, including Linux (direct and parport), Win32, Script, Dummy, and more. It also contains a number of direct access devices including an example printer and a relay controller card.
GNU Phantom.Home is a computer controlled home automation system. The software includes a circuit diagram for building the Phantom.Home.Controller, a simple circuit board that attaches to your PC's parallel port. Using the combination of hardware/software you can control (i.e. flip on or off) nearly any 120V device. And with a little bit of electronics know-how, you can probably control nearly any device at any voltage by modifying the circuit board to meet your needs. The simple circuit included can be created and built for around $25. The modules cost around $10 (basically a heavy duty relay).