I have a workplan for each week in my independent study. I've reserved the three weeks from September 24 until October 14 to define which program I'd like to use as a case study.
While I might defer thinking about this problem, as it happens I've started to consider what factors would go into a good program for a case study. A few thoughts:
I want to avoid open source programs that serve a very limited audience. Typical examples in this space are programs written by developers for other developers. GNU Emacs is one such program: an extensible, customizable text editor that is mostly used by developers. Similarly, "integrated development environments" (IDEs), debuggers, and other programmers tools serve a limited, highly technical audience. Special tools such as FreeDOS XFDISK, while geared for all FreeDOS users, are limited in scope and would not provide an interesting usability case study.
Similarly, simple programs would yield very limited results, and likely would not apply to even moderately-sized programs. Therefore, I exclude general text editors such as FreeDOS EDIT and GNOME's gedit. Also: games and desk tools such as calculators.
On the other extreme, I would avoid programs that are overly complex or have very deep menus. I need to keep a manageable scope of this independent study, and programs like OpenOffice, LibreOffice, or even Firefox that have rich menus would expand the usability tests to a point where the results may not be applicable to other open source programs.
Icons are an important part of usability, and today's graphical programs often leverage some icon set to represent program actions. Typical examples are a "toolbar" of commonly-used activities, such as "copy" and "paste", or "bold" and "italics". I prefer to leave icons for possible inclusion in this study. That means I will avoid programs that exist solely in text mode, or other programs that do not make use of icons: FreeDOS XFDISK and EDIT (also mentioned above) and many file managers.
The right open source program for this usability case study would need to strike a careful balance: generally useful to a wide audience, not overly technical without becoming trivial, not too many menus, and some icons without being purely icon-driven.