Philip Johnson proposes Three Prime Directives to guide open-source software development. While provided as goals for developers to aim for, Johnson claims that the developer of a system cannot verify whether their own system actually achieves these goals. Only an external user or developer can do this.
As an example of using the Three Prime Directives as a framework for software review, here is my own review of Timmon Time Monitor. I've actually been a Timmon user for about four years now. Unable to explain how many of my days seemed to get away from me without much to show for it, I searched for a good time tracker program. Of the three or four programs I eventually downloaded and tried, Timmon was my favorite.
PD1: The system successfully accomplishes a useful task.
I think the reason I finally settled on using Timmon is that it is fairly simple. It does exactly what I wanted in a time tracker. I can define my own hierarchy of activities or projects. Then, with a click of a button, I can start tracking time for any of those activities. Another click of the same button stops the timer. It is also easy to edit the time spent on a task, to add a complete task that covers a given time period, or to add a comment describing the work done on a task.
It is then possible to view the accumulated time for all activities at different levels of the hierarchy. For example, I have a Personal category that includes Emailing and Surfing. For the current day, week, month, or year, I can easily see the total time spent either Emailing or Surfing. I can also see the total for both activities combined, plus any other activities I labelled as simply Personal.
Here's a screenshot of Timmon in action:
Timmon has a couple extra features I don't use, such as reports or setting the max time for a given activity.
PD2: An external user can successfully install and use the system.
It's been a while since I installed Timmon, so I had to revist the process. The project homepage lets you try Timmon as JNLP program, so, assuming you don't mind visiting the website every time you wanted to use Timmon and you don't mind giving the self-signed web application full access to your computer, it's actually possible to run Timmon without installing it all. This is a pretty nice feature. When run this way, Timmon still saves its time record in a number of XML files in a .timmon directory in your home folder, so this is a viable option for a novice user.
Installing is a little tricky because the Timmon project provides both a .zip and a .tar.gz. However, the .zip is damaged and unopenable, so you have to be able to unzip a .tar.gz on your system. Also, running the program requires executing a jar file. I think this is foreign to many users, though the main project page provides fairly clear instructions on how to do so.
The Documentation link from the project home page is broken. The project README file included in the download mentions a .pdf manual that doesn't exist. However, the download does include an HTML manual. The manual basically covers the program menus and buttons, so it doesn't add much beyond what could be learned by simply exploring the program. I think Timmon's interface is fairly self-explanatory, though; I don't think I ever used the manual when I initially installed it.
PD3: An external developer can successfully understand and enhance the system.
In the four years I've used it, I have discovered a few little bugs. For example, if I close Timmon while tracking time for a particular activity, Timmon will resume tracking for that task every time I open it. I have to delete the task and restart Timmon to break it of this. So I was interested to see how easy it would be to modify the program.
The project has been dead for about four years. The project README that it is included in the download explains how to build the project manually or by using Ant. The source code for the current version of the project is supposed to be in the damaged .zip file and so is not currently available for easy download. It is still available for checkout from the sourceforge CVS, though.
Browsing the CVS reveals that the code is well-formatted and well-documented with javadoc comments. So it would be easy to extract a javadoc overview of this project's files. However, I did not find an overview document intended for a new developer. There are a number of packages and classes here. Based on the README, the project also builds on 5 separate open-source libraries. With no high-level overview, it would certainly take a fair amount of work for a new developer to build a mental picture of how this program is structured.
In conclusion, I think Timmon clearly satisfies PD1 (does something useful). It does fairly well on PD2 (easy to install and use)--the .zip file and documentation link just need to be fixed. Though well-documented, Timmon needs to provide a short introduction or overview document for a new developer to really satisfy PD3 (easy to enhance).