At the basic entry-level, not a lot.
All new divers need to learn the same basic dive theory and skills, so nearly all the major training agencies use near-identical basic training techniques and entry-level course syllabuses (and durations). The resultant 'Level 1' certifications therefore all place similar limitations on newly-qualified divers, regardless of agency (must dive with a buddy, no deeper than 18-20 m depth, non-decompression dives only, etc.).
PADI IDC Gili Islands