This application runs on Yosemite (OS X 10.10), written entirely in Swift including ported code from Objective-C, based on the discovering and development efforts of Matthew Robinson to use an Apple computer running Mavericks (OS X 10.9) as an iBeacon transmitter (originally written in Objective-C), you can read more at Mavericks as an iBeacon.
Here is the advertisement data to start broadcasting as an iBeacon:
Source code published on GitHub.
Note: Despite to the fact that many forums are saying that you cannot use Yosemite as an iBeacon, I can confirm that this solution is working with an external Bluetooth 4.0 (BLE) USB dongle.
Recommended Bluetooth dongles: