Except is a preposition meaning 'not including'; as, All the boys except Ram went there.
Excepting is the participle of the verb to except and means 'leaving out', 'excluding'. Excepting is not interchangeable with except and is used in the negative only (=not excepting, i.e. including). Thus: All boys, not excepting (=including) Ram, went there.
Except for is used to denote 'what is excluded is different from what is included'. It indicates an 'exception to a general condition'. Thus All his sons are well established except for the youngest one. Except that means 'apart from the fact that. Thus : She is a good student except that she is sometimes careless.