Your own web server utilizing another, then dealing with user credentials, assignments, and launching of courseware would be a tough one. These systems essentially have a Runtime API that manages the student attempt SCORM Interacts with.
There are a few parts of SCORM support that you'd obtain from Rustici's SCORM Engine that are actually worth paying for.
- 100% SCORM Compatibility (1.2, 2004)
- I believe they have a .NET and Java implementation (uncertain about PHP) that you can plug into your platform. If you don't use those languages I'm sure they'd be grateful to answer any questions you have on further support.
- You're covered on importing PIF/ZIP Content Aggregation Model packages. Even the robust ones.
- SCORM Cloud hosting could negate the need for the SCORM Engine (#2)
The main reason you can't find much free in this space (with the exception of moodle) is mainly that is a epic amount of work, and another main reason you find many platforms with mixed support of SCORM. There is also the legacy space, and aged antiquated stuff that also comes to that end.
In the end you have the Runtime, Content Package Parsing, and if your using SCORM 2004 all the sequence and navigation rules. Those 3 things don't sound like much, but they are an exhausting amount of work from scratch.
Hope that all made sense,
Mark