What qualities and characteristics make for a "good" piece of open source software? And once that question is answered, then what pieces of library-related open source software can be considered "best"?
I do not believe there is any single, most important characteristic of open source software that qualifies it to be denoted as "best". Instead, a number of characteristics need to be considered. For example, a program might do one thing and do it well, but if it is bear to install then that counts against it. Similarly, some software might work wonders but it is built on a proprietary infrastructure such as a closed source compiler. Can that software really be considered "open"?
For my own education and cogitation, I have begun to list questions to help me address what I think is the "best" library-related open source software.  Your comments would be greatly appreciated. I have listed the questions here in (more or less) personal priority order:
* Does the software work as advertised?
* To what degree is the software supported?
* Is the documentation thorough?
* What are the licence terms?
* To what degree is the software easy to install?
* To what degree is the software implemented
using the "standard" LAMP stack?
* Is the distribution in question an
application/system or a library/module?
* To what degree does the software satisfy some
sort of real library need?
What sorts of things have I left out? Is there anything here that can be measurable or is everything left to subjective judgement? Just as importantly, can we as a community answer these questions in light of distributions to come up with the "best" of class?
'More questions than answers.
 There are elaborations on the questions in a blog posting. See: http://tinyurl.com/ybk2bef
Eric Lease Morgan