"None", although a pronoun, could be considered a substitute for the number zero:
- Two of my children are boys
- One of my children is a boy
- None of my children are boys.
It doesn't just relate to people - it can be used for anything.
"No one" means 'no person', so that can only relate to people. The "one" here acts like the pronoun 'one', and not the number one. The word "no" is the determiner. As such, it is used differently to "none" and is not interchangeable.
- I invited all my friends, but no one came.
- I thought I heard a knock at the door, but there was no one there.
There isn't too much difference between "no one" and "nobody", but style guides suggest that 'no one' is the preferred singular pronoun for academic or professional writing, while 'nobody' is considered more informal.