Look in the root directory and you will see a Developer folder. The most interesting stuff is in there (ProjectBuilder, InterfaceBuilder, etc).
There are various other things (compilers, headers, libraries, et al) scattered all over the rest of your hard drive.
The bom (bill of materials) used to be (in NeXTStep times) an ascii text file that listed everything in the install -- it now appears to be ascii mixed with some binary so there is probably a tool (command-line??) that will allow you to read it.
I'm not at my system right now so I can't check -- I'll post another message as soon as I figure out how to read the bom.