The CM11A is a device built by the X10 company for controlling
devices by sending signals through the power lines. It's a small
box that plugs into an AC outlet and connects to a serial port.
The CM11A is shipped with Windows software.  Heyu2 will control your
X10 devices, set the CM11A interface clock and monitor X10 signals
on the AC power lines. It will upload macros and timers to your
CM11A for stand-alone execution.  Heyu also supports the CM10A and 
the CM12U.

In addition to the CM11A, heyu supports W800RF32A or MR26A RF receiver
connected to a second port as an auxiliary input device for X10 RF signals.

Heyu can also use an optional CM17A interface to transmit X10 RF signals. 

WWW: http://heyu.tanj.com/heyu2/