Development system used was only a text editor and compiler.

In 1964 the very first IDE (Integrated Developer Environment) was created for Dartmouth BASIC. This marked the beginning of the end of developers painstakingly designing applications on paper and using multiple unrelated applications to keep track of everything and yet another unrelated application to actually enter the code so that one last application (the compiler) could process it (then it went to debugging and onward, but that's other subjects). In 1975 Maestro I made this technology generally available to the public rather than such tools being hidden deep with the inner workings of developer companies or university computer systems. Visual Programming was pretty much the death nail for exclusive text-to-compile operation. Although developers would continue this way of doing things with assembly language, they to usually migrated to assemblers offering the equivalent to an IDE. So, after 1975, using a non-extensible text editor that is not part of a larger development application is rare.

Hint: emacs is extensible, vi is pretty much not.