What is the Silicon Labs Proprietary Flex SDK and where can I find more information about it?

The Silicon Labs Proprietary Flex SDK is a complete software development suite for proprietary wireless applications. Per its namesake, Flex offers two software implementation options and paths:

• RAIL (Radio Abstraction Interface Layer) is an intuitive and easy customizable radio interface layer designed to support both proprietary and standards-based wireless protocols. It simplifies and accelerates the development process. This is the lowest layer available for all networking stacks in the Bluetooth Gecko SDK (GSDK).
• Connect is an IEEE 802.15.4-based networking stack designed for customizable broad-based proprietary wireless networking solutions that require low power consumption and operates in either the sub-GHz or 2.4 GHz frequency bands. This solution is targeted towards simple network topologies.