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 iPhone 5s. It was also seen on several other prototypes, one of which was a PVT (Production Verification Testing) unit. It also seems to be extremely similar to InnsbruckNanshan 11A24580o.
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: