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.
PAUS is a system for controlling stuff with simple event-based Perl scripts. It can be used for controlling your house, creating an alert system, or making a remote controlled mp3 player. It is a flexible project that "merges" other I/O projects together, such as lirc (remote control), lcdproc (LCD output), mpg123 (mp3 player), and various I/O boards (such as the K8000). It's modular, extensible, multi-threaded, and has networking support.
jukebox-control includes a Linux driver module for an easy/dirty cheap to build DIY parallel to the Sony S-Link interface, plus Perl modules with both control-A1 (II) and control-S protocol implementations. Its actually-incomplete development state makes it interesting for developers mostly.
jHomenet is a home automation application. jHomenet uses both X-10 and Dallas Semiconductor 1-Wire network sensors and devices to collect sensor data and control devices. jHomenet can be programmed to respond to events, including particular sensor data values or time-of-day events.
MoCo is a system that monitors and controls SCADA points, such as temperature, HVAC, power, lighting, sprinkler systems, and more. It has industrial capabilities, but is scalable from very small home systems to enterprise, world-wide ones. It works with inexpensive I/O bridges (including X10, Insteon, and 1-wire) from a number of manufacturers. It has sophisticated history logging and diverse control capabilities, as well as a 117-page implementation manual.
domus.Link is a Web-based frontend for Heyu. Its design focuses on separating configuration from actual controls, thus giving the user a simple and user-friendly GUI. The primary concern is that anyone with little or no knowledge of home automation systems can easily manage and administer the system.