Freevo is an open-source home theatre PC platform based on Linux and a number of open-source audio/video tools. MPlayer and/or Xine can be used to play audio and video files in most popular formats. Freevo can be used both for a standalone PVR computer with a TV+remote, as well as on a regular desktop computer using the monitor and keyboard.

MythTV is a homebrew PVR project that I've been working on in my spare time. It's been under heavy development for almost four years, and is now quite useable and featureful.

LIRC is a package that allows you to decode and send infra-red signals of many (but not all) commonly used remote controls.

WinLIRC allows you to transmit and receive standard infrared remote control signals. This allows you to control your computer using almost any standard infrared remote control. It also allows your computer to control other equipment which uses these signals (stereo equipment). WinLIRC is the Windows equivalent of LIRC, the Linux Infrared Remote Control program. WinLIRC (through version 0.6) was originally written by Jim Paris. Later releases are written and maintained on sourceforge.