Is assembly the only low level programming language, and if not is it the most widely used?

I've started learning assembly recently and as I've looked across the internet I see more and more people saying that assembly is not useless, but it's also not worth the time to program things in a language that requires such time and effort compared to high level languages. Is the efficiency between a high level language program and a low level one really not even noticeable enough to pay attention to nowadays, and is there another low level language like assembly that is more widely used?