Multi-protocol and proprietary application development can be based on Nordic Semiconductor's own Gazell and Enhanced ShockBurst protocol reference code and application examples.
Gazell
Gazell for the nRF51 series is a lightweight, low power, and easy-to-use protocol with advanced coexistence features especially suited for wireless desktop products and other power-sensitive wireless applications. It is on-air compatible with Gazell on Nordic's nRF24Lxx ICs, and can share an nRF51 series device with a Nordic SoftDevice.
Enhanced ShockBurst
Enhanced ShockBurst (ESB) for the nRF51 series is a simple, lightweight protocol, that is on-air compatible with Nordic's nRF24Lxx devices. ESB for the nRF51 series provides a simple upgrade path for nRF24Lxx based applications.