File types in EFI partition
I don't expect that you're going to find apps that you can run since everything in the EFI partition is presumably dealing with the hardware directly and doesn't conform to a UNIX/BSD/OSX application model. Instead, it is a bit of a mini-OS that has enough drivers to support booting from various devices (disk, USB, network, etc.) before handing control over to the "booted" operating system.

That all being said, I would imagine that the files you'd find there would be a combination of the raw boot code (i.e. initial bootstrap of UEFI "mini-OS"), the main UEFI kernel, various device drivers for the hardware onboard, NVRAM storage and possibly a driver/API that the OS can access to communicate with the above (e.g. setting nvram values).

That all being said, I'm sure there are better resources out there on the internet to explain what the exact files are, but I would suspect that there is extremely limited utility for end users since it is all very hardware specific ultimately.