Looks like he removed the LED of an EOTech-lookalike reflex sight and replaced it with a small LCD screen, hooked up to a small microcontroller which has some custom software on it and is hooked up to the sight buttons. So, he now has a little custom computer screen, projected out at (probably) 100 yards by reflex optics, which he can display whatever he wants on. This means custom reticules, etc. As alluded to in his description, he could add a round counter and other bells and whistles.
Cool idea. Awesome to see people pushing the limits of expectation in the firearms world.
It's not a hologram, so it won't have the "break the glass and still run with a shard left" feature, but neither does any normal red dot sight like Aimpoint. Main question is how it will hold up to recoil and other abuse.
EDIT: Sorry, if you can't tell, I'm an EOTech guy. EOTech's are projected out at 100 yards. Reflex sights are usually projected at infinity, so that's probably what this is projected at.