I used Turbo Pascal version 4 or 5 as a contractor on a government site in the late 1980s. That IDE made me so much more productive than the command line compilers of the day. Being taken immediately to your syntax error so you could fix it and recompile at the touch of a button spoiled me. I also liked the fact that you could have the default runtime error checking to find more subtle errors and then disable that checking to speed your program up after those errors had been found. I moved from that back to command line compilers and makefiles on a Sun workstation. It prompted me to create an ugly little shell program to run make and look for the error message if the build failed. It was the closest I had to a proper IDE for quite some time after that.

I believe Mac OS X recognizes executable files in much the same was as Linux/Unix does, via the file permissions. Here's the file permissions for the Mail program.

ls -l /Applications/Mail.app/Contents/MacOS/
total 11648
-rwxrwxr-x 1 root admin 5962096 Jun 16 15:18 Mail