Multiplexed video cams
I have one bt848 video capture card in a computer, but I wanted to connect a few video cameras at once. I used a MC14052BCP analog multiplexer chip and two pins on a parallel port to let my camera software flip the video input before grabbing a frame.
When I'm looking at live frames from a camera, I can click a button to save a snapshot. Button clicks result in an ajax HTTP call from the browser that is forwarded to a snapshot service which fetches a new frame and write it to disk.
Code is here. This is a web server that fetches preset resources from other web servers and saves them into files according to templates. On my camera viewing pages, I simply put POST forms that request that a picture is saved. The httpsnapshot service grabs a jpeg frame, saves it into my photo area, and my photo site notices the new file automatically.