Okay... well, most of the stuff I've put up on the web that is Apple related is pretty dated at this point, but I think it can still convey the basic ideas. The older, more historical stuff is (of course) meant to be old.
Some of the best aspects of NEXTSTEP/OPENSTEP to be carried over to Mac OS X was the Services and Bundled Resources, two articles I've written on those subjects can be found here:In addition to most of the general aspects of NeXT you can find elsewhere, Sun/ORACLE still has a ton of manuals in their documents archive from when they were partnered with NeXT and were attempting to make Solaris into NEXTSTEP like environment. You can learn a lot about how NEXTSTEP/OPENSTEP worked in these documents.That should give a general feeling of where Mac OS X was coming from when Apple bought NeXT. A nice visual display of NEXTSTEP in action is this demo which a friend of mine in Germany copied from his video tape.One of my favorite apps, which I use in a lot of the talks I give as a demo of how Mac OS X can help grow applications, is TextEdit. Most people when they see TextEdit start up would quickly dismiss it as a simple text editor and little else. But with services (both system services and third party services), you can extend TextEdit into a very nice word processor (it is the only word processor I use). I wrote a small article on the pre-Mac OS X version for my Rhapsody site:And another article for TextEdit back in 10.2:... which is a little dated. I looked at the history of TextEdit through 10.4 in this article:Things have changed a lot in 10.5/10.6, but this all sort of gives you an idea where these aspects of the current OS evolved from.
Two of the system wide services provided by Apple that I think are the most helpful to developers are the text services and color services. This is a great write-up on the vast improvements Apple made to text services starting in Mac OS X v10.3:And color services here:I did a smaller article on the color services with Rhapsody here:That covers most of the type of stuff that I talk to people about when speaking before Mac User Groups and the like. In the original Mac OS, developers were on their own when it came to most of these types of things, and you would see many different implementations of them from application to application (and you still do in most Carbon applications today). But if you are starting from scratch building a new application in Mac OS X, there are tons of things that pre-exist that you can use so you can spend more time on the core functionality you want your application to accomplish.
A friend of mine had a image editing application back in the NeXT days, and it was available on Mac OS X years before Photoshop, but was never able to compete directly with it. Apple bought all his technology and turned it into Core Image which other developers could use (another friend of mine was the first to do that with this application), and Apple later made Aperture based largely on all that.
That was most likely more information than anyone wanted on this subject... sorry for rambling on.
