This article discusses software internally used by Apple.
Acquiring a copy without Apple's consent is illegal and may result in being scammed.
This is a firmware based on an internal version of iOS 7.0, originally seen on an PVT (Production Verification Testing) iPhone 5s. It is very similar to other 7.0 NonUI versions.
This firmware has the kernel version
Darwin Kernel Version 14.0.0: Tue Aug 13 21:48:05 PDT 2013; root:xnu-2423.1.73~3/DEVELOPMENT_ARM64_S5L8960X.
Upon booting, SwitchBoard.app will let you choose from the following: