theChiChen has created a new Github project with some hello-world-level UEFI applications. Besides a few Hello Worlds, there is are Stall and ResetSystem commands. These are built with EDK-II/Tianocore, not GNU-EFI toolchain.
https://github.com/theChiChen/UEFI_SHELL_Utilities
https://github.com/theChiChen/UEFI_SHELL_Utilities/blob/master/ChiChenPkg/Application/Stall/Stall.c
https://github.com/theChiChen/UEFI_SHELL_Utilities/blob/master/ChiChenPkg/Application/ResetSystem/ResetSystem.c
One of these days, I need to create a list of all these hello-world apps for UEFI and other firmware targets. There used to be only a handful, now there’s a few dozen..
Firmware Security 