In a previous posts, I mentioned the need for a list of open-source software that would be listed as recommended study for programmers. It would seem that the first step is to list some of the possible candidates. Wikipedia has a list of open source software packages that makes a good starting point.
The next step is to list some basic requirements for inclusion in the list. The target audience should mainly be the undergraduate student of Computer science, although good examples of well crafted source code will be of interest to a much larger group. This puts some bounds on the size and type of software project since not all can reasonably be studied in a typical programming class. Let's assume a university course with the proposed title of "Survey of Real World Software." Prerequisites for the course would include familiarity with several common programming languages such as C, C++, and Java. New and relatively esoteric languages such as Python, PHP, and others are not usually a part of a standard CS curriculum.
I believe that modern graphical user interface (GUI) code requires a separate course of study due to the specialized nature of event handling. The same is true for most kinds of network or website applications. What is needed is a relatively small, yet useful software application that concentrates on delivering specific functionality. This would seem to apply to small compliers, server applications, and other batch processing tools. The GNU/Linux command line tool suite should be a fertile ground for this programmer's garden.
One example that comes to mind that I have personally learned a great deal from is the PL/0 compiler created by Niklaus Wirth in 1975. At 790 lines of Pascal, it is a marvel of elegant efficiency. If you prefer, there are some C translations here in 490 slightly more packed lines. This is an excellent introduction to parsing, among other things.