Besides, except and apart from

These expressions are sometimes confused. Besides usually adds: it is like saying with, or plus (+):

Besides the violin, he plays the piano and the flute. (He plays three instruments.)

Except subtracts: it is like saying without, or minus (-).

I like all musical instruments except the violin.

Apart from can be used in both senses:

Apart from the violin, he plays the piano and the flute.

(= Besides the violin...)

I like all musical instruments apart from the violin.

(= .. except the violin.)

After no, nobody, nothing and similar negative words, the three expressions can all have the same meaning.

He has nothing besides / except / apart from his salary.

(= He only has his salary.)