By popular demand (shocking, I know), MCE Controller now supports RS-232 in addition to TCP/IP connections. This means that you can now control any Windows PC via the serial port.
MCE Controller is an open source application I built for my home control system. It makes it easy to integrate Windows PCs with other devices and control systems. Any device that can send strings over TCP/IP or (now!) a serial port can now send commands to a PC running MCE Controller.
For example, sending ‘up’ causes the equivalent of an up-arrow keystroke. Or sending ‘screensaver’ causes the Windows screen saver to kick in on the target PC.
You can simulate mouse, keyboard, and Media Center remote control input. You can start applications, change windows’ z-orders, and even invoke Windows system functions (e.g. shutdown, standby or hibernate). MCE Controller is extensible as well, allowing you to define your own commands.