The IRClone-MX was a device that you could use to program an MX-500 (or MX-600) from a PC. It relied on the MX-500's ability to clone itself to another MX-500. Mike (the developer of IRClone) captured the IR data stream between the two MX-500's during the clone operation. First, he was able to backup an MX-500's configuration onto a PC. Then after careful reverse-engineering, it was determined how to edit the data before sending it back to the MX-500, thus giving the ability to PC-program the MX-500's configuration.

Mike teamed up with a fellow named Dave who wrote a windows editor for the device. They went into business selling the IRClone-MX and the 500e editing software.

This was back in 2002. After shipping about 1500 of the devices, they stopped making them around 2004. By that time, the URC PC-programmable remotes such as the MX-700, MX-800, etc. had really taken off and they figured (or perhaps witnessed) that the market for PC-programming MX-500's had tapered off. They put up a final version of software onto their website that didn't need an activation key, and have since disappeared.

The website stayed active until the summer of 2006, then it went offline. However, you can still see a bit what it looked like by using archive.org.
[Link: web.archive.org]

Every once in a while, an IRClone-MX box will come up for sale in the Marketplace forum or on ebay. They tend to go for about $75. The software is still available, but is not useful until you obtain an IRClone-MX device.