All the major Canadian airports also have the US customs and immigration on-site. You go through it as part of the standard airport security process and then the airplane goes to a domestic terminal when it lands, as if the flight had originated within the US. You get off the plane, grab your luggage and leave, no additional lines, security, talking to officials, etc.
The only European airport that does this is Dublin, last I checked.
You can use eGates in the UK, same as me as a British citizen (as long as your passport's new enough, probably all of them by now) - that covers it doesn't it? Otherwise I'm not clear what 'pre-clearance' is skipping? Painless for me into Canada too.
Americans can _often_ use eGates into the UK - but the same set of exemptions apply as to British citizens using them. For example, if you're traveling with children under 10, you can't.
However, as others have pointed out, this isn't what pre-clearance is. It's more akin to clearing French passport control and customs in Dover or rather than Calais, and can make the trip substantially shorter than it might be otherwise.
When I still lived in the UK, I found it quicker and more pleasant to fly from Heathrow (or Bristol) to Dublin and then on to the US having cleared immigration during the layover. It's also quite a bit cheaper when you fly from the UK in a premium cabin since Ireland doesn't have the egregious air passenger duties that the UK does.
The portion of Dublin airport that has flights to the US is officially American soil. You deal with customs in Dublin airport, and then arrive to a domestic terminal at your US destination. It's very helpful.
The only European airport that does this is Dublin, last I checked.