volume and pager
Half the desk. See the three red lights in the shelf? The bottom one is the pager. The upper monitor is for my other workstation. It shows logs and other things I always want visible. The monitor to the right displays video.
This is the box that the bottom red LED is on. It's a hand-made panel with 8 buttons which are encoded to 4 wires with a poor man's multiplexer circuit (a bunch of diodes). Pressing a button will change the signals on the wires. That signal is read many times a second by the K8000 board (see below). The reader software notices a request on those inputs and opens a socket to my main workstation. There, an fvwm2 plugin answers and listens for the desktop number to switch to. I also have Ctrl-Shift-arrow mapped to change desktops, so I use that a lot since it's closer (and available on the machine at work too).
This is a farther and higher view than the previous picture's. You can see the whole K8000 board here, along with two little experimenter boards that contain additional control circuits. Part of the board is obscured by waxed paper on plexiglass. There's a hole in the shelf for a cable to go through, and I'm able to get a pinhole camera projection of the front yard through the hole. There's also a telephone punch block visible in all these pictures. When I had even more lighting and sound control wired up (in previous residences), I used that to organize the cables running everywhere.
There's one more active circuit, which you can hardly see. At the far right, against the monitor, there's a voltage divider that scales down the level on my telephone pair. That's fed to one of the optoisolators on the K8000 (in fact, it's why there's a red light on in the middle of the K8000 board). When I pick up the phone, that LED turns off and the polling computer notices that the phone is off-hook. Via some tiny client / server python programs, the polling computer is able to fade down the music on the music-playing computer when I pick up my phone. Phone rings are also trackable.