Eddystone is a protocol specification that defines a Bluetooth low energy (BLE) message format for proximity beacon messages. Eddystone currently consists of 4 formats: Eddystone UID, EID, TLM, and URL.
The Physical Web is based solely on the Eddystone-URL format, which is unique in that it is a Web protocol. The iBeacon and the other Eddystone protocols are all app protocols. Eddystone-URL gives the Web the new dimension of proximity, while the other 4 protocols do the same for apps. The Eddystone source code is available for anyone to download from Github.