There never was a fee, but back in the pre-OS X era, Apple's Macintosh Programmer's Workshop (MPW) system was sold as a commercial product. Several other development systems were also available, like MetroWerks Code Warrior.
Since Mac OS X was released, Apple's software development tools have been available for free. They are included with each Mac computer, and each OS X upgrade. The tools are also available for download, at the location Swordmaker mentioned above.
It is not necessary to pay any fees to obtain the development tools. The fee-based developer programs that Swordmaker mentioned above include extra services, e.g., early access to beta code, direct support, etc., which are not requirements for many developers.
Apple's IDE is XCode, described here - http://www.apple.com/macosx/developertools/xcode.html
Most applications are developed in Objective-C language with the Cocoa framework (formerly known as NeXTSTEP), and several other programming languages are supported too. The tools include debuggers, screen design applications, etc. The compiler used in XCode for languages like C, C++ and Objective-C is the same one used in Linux: gcc.
XCode with Cocoa is certainly one of the best software development environments available today.
So is Fortran IV still around?