Because there is no open and interoperable specification for proximity beacons, Radius Networks has authored the AltBeacon specification as a proposal on how to solve this problem. The AltBeacon specification defines the format of advertisement messages in an attempt to bring a standard platform-independent way for proximity beacons to broadcast.
This is unlike the iBeacon specification, which requires the vendor to register with Apple's MFI program in order to find out the exact Bluetooth advertising channel protocol data unit (PDU), which iOS devices look out for.
The AltBeacon specification defines the format of the advertisement message that BLE proximity beacons broadcast and is free for all to implement with no royalty or fees.
Keep an eye out for AltBeacon implementations. I'm sure they'll come thick and fast with third-party library implementations very soon.