The problem with the really cold stuff is obviously LN... I wanted to know if there is anything you can get with like closed loop refrigeration and electronics. I can call that open loop for the LN2 or He.... those are like gasoline appliances compared to electronic devices. I know you can buy a dewar etc... its just a different world when you need god damn liquified gas in thermos. I don't like how it evaporates it really bugs me that you can buy it and then it slowly decays its like paying a tax.
Liquid nitrogen isn't even expensive; we're talking about euro or two per kilogram of nitrogen, or about the price of milk or fruit juice, when you have a proper contract with a supplier. (As a liquid, its about 80% as dense as liquid water.) The flasks are designed to leak, because that makes them safe –– no pressure buildup! ––, and three quarters of air is already nitrogen so leakage is not an issue. They have a simple very loose stopper, and that is enough for a double-walled dewar flask. Just ensure good ventilation, so you keep acceptable oxygen ratio in the ambient air.
You really need to think of it as liquefied air with the other gas components removed. That's how it's produced, too.
To cool something with liquid nitrogen, you can simply continuously boil the setup in nitrogen.
With liquid nitrogen, you can seriously overclock processors. It matters for single-threaded performance for non-parallelizable non-distributable tasks (including cryptographic hashes).
Germanium, silicon, and gallium arsenide band gap energy all increase by 0.3eV - 0.8eV when temperature drops from 300 K (room temperature) to 77 K (what you get when you let nitrogen boil at one atmosphere pressure continuously). Thermal (Johnson–Nyquist) noise in e.g. resistors is halved, from \$0.129 \sqrt{R} \text{nV} / \sqrt{\text{Hz}}\$ at 300 K to \$0.065 \sqrt{R} \text{nV} / \sqrt{\text{Hz}}\$ at 77 K.
Alloys benefiting from annealing can become even better (stronger and harder, with fewer lattice defects) at such temperatures; see
cryogenic treatment. Most flexible rubbers and plastics lose their elasticity, though. (It is one way to machine otherwise too elastic materials.)
Both yttrium barium copper oxide (YBCO) and bismuth strontium calcium copper oxide (BSCCO) practical superconductors have critical temperatures above liquid nitrogen boiling point, and are quite well researched, so if one is sufficiently interested in superconductors these and liquid nitrogen is a valid starting point, with first- and second-generation conductors, 1G and 2G wires, commercially available.
These are the use cases I know of; I'm sure there are others. I
think N-MOSFET drain-source resistance at full conductance decreases, but the gate-source threshold voltage increases as temperature decreases, with total gate charge remaining approximately constant, for example.