Thanks to pcwzrd13 for supplying a copy of this program for the Commodore 64/128.  Included in the archive is also some technical documentation on the hardware, interface and programming.  You can find a thread with more details over at Lemon64 Here. The following is from an advertisement that explains what you can do with the X-10:

THE X-10 POWERHOUSE INTERFACES WITH YOUR COMMODORE TO CONTROL YOUR HOME... FOR SECURITY, COMFORT AND ENERGY SAVINGS.

This remarkable Interlace lets you run your home through your Commodore 64 or 128 and a Keyboard or joystick.

When you're away, it makes your home look and sound lived In. When you're home, it can tum oft the TV at night and wake you up to stereo and fresh brewed coffee in the morning. It can even turn on your air conditioner and control your heating.

SPECIAL COLOR GRAPHICS MAKE PROGRAMMING A SNAP.
You simply pick a room from the display screen. Use your keyboard or joystick to position graphics of lights or appliances Then follow on-screen instructions to program any light or appliance to go on or off whenever you choose. You can even control thermostats, light intensity and more.

THE WAY IT WORKS. The X-10 Powerhouse Interlace is cable-connected to the Commodore "User" port and plugged into a standard 110V outlet. After it is programmed, the Interface sends digitally encoded signals through your home wiring to special X-10 Modules. To control a lamp or appliance, you simply plug the electrical device into a Module and then plug the Module into an outlet. The Interface can control up to 256 Modules throughout your home and won't interfere with normal use of lights and appliances.

There are plug in Appliance Modules, Lamp Modules, Wall Switch Replacement Modules and Special 220V Modules for heavy duty appliances such as water heaters and room air conditioners. Plus Thermostat Controllers for central heating and air conditioning. Telephone Responders to control your home from any phone, and much more.

IT WON'T TIE UP YOUR COMPUTER. Use your computer only for programming. When you're finished, disconnect the Interface from the User or RS-232 port and keep it plugged into any convenient power outlet in your home. It will operate as a stand-alone controller with battery back-up and will run your home automatically.