Export pump all schemas except Sytem related schemas
As @a_horse_with_no_name mentioned, you can use the exclude parameter to limit the objects to be exported.

It's very simple to use and it supports in/ like... operators.

Usage example:

expdp username/password directory=datapump dumpfile=x.dmp logfile=y.log full=y exclude=schema:"in ('SYS', 'SYSTEM', ..., ...)"