Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!

Nil represents an emptry List of anything of zero length. It is not that it refers to nothing but it refers to List which has no contents. In other words, Nil is equivalent to List() or List.empty.

Null is a Trait and null is an instance of Null, which is similar to null in Java.

Nothing is a Trait. It is a subtype of everything but not superclass of anything. There are no instances of Nothing.

None is used to represent a sensible return value, which is a way to avoid null pointer exception. Option has exactly 2 subclasses: Some and None. None signifies no result from the method.

Unit represents type of method that does not return a value of anys sort.

Any is the supertype of AnyRef and AnyVal. AnyRef is the supertype of all the reference classes (like String, List, Iterable) in scala. AnyVal is the supertype of all the value classes (like Int, Float, Double, Byte, Short..). Null is a subtype of all the reference classes. null is the only instance of Null. Nothing is subtype of every other type i.e of reference and value classes.

Think- AnyRef == Object in Java.

Ref

http://oldfashionedsoftware.com/2008/08/20/a-post-about-nothing/