mythtv is a brilliant piece of open sourse software that ties together a TV tuner card, a Linux-based PC, and free Internet listings services to build a high-powered PVR, like a TiVo with far more bells and whistles. For example, a mythtv box can be used in many countries around the world (including the UK and Canada), and it stores its files in a format that is intended to be copied for use on other devices, so it's a snap to burn a CD with a bunch of your favorite programs to take on plane journeys, or to email clips to friends, or to drop incriminating CSPAN/Question Period footage in your file-sharing folder and foment revolution. It's also free to operate, and can be upgraded easily, and shares all the other properties of a general-purpose PC (so your set-top box can also be your WiFi router, firewall, and all-round file-server).
However, like many open source software projects, installing and configuring mythtv isn't for the faint of heart. This HOWTO is a good step in the direction of making mythtv accessible to the masses.
(via Wasted Bits)