I made a MySensor gateway node that works as a bridge to an existing X10 system. It allows to control the X10 light and appliance modules from the home automation software. The setup consists of a X10 remote which has been modified so that the digital signal from the gateway keys the transmitter. The X10 controller then receives the data package and does it's thing on the AC line to control the switches. Any existing X10 remote or alarm sensor can be used. I had an old key-fob with broken buttons that became the donor transmitter. When hacking the remote one looks for the signal from it's IC that normally keys the transmitter and disconnects that to feed the signal from the MySensor node instead. A scope is handy to find which pin is the right one.
The GIT with the Arduino script for the Gateway/X10 controller can be found at [https://github.com/garyStofer/MyMySensors2.1] . The X10 house code is hard-coded to 'A" and I limited the number of switches arbitrarily to 12, but the avid Arduino enthusiast will quickly see how to modify the code to suit. It is not necessary that the X10 part be implemented on the MySensor gateway, it could just as well be done on a separate node.
If there is any interest I will add some pictures and schematics.