The GNU utilities and the Linux operating system are of high software quality. The free distribution of the software and the accessibility of the source code seems to motivate many users to contribute bug reports, patches, and enhancements. Also any GNU or Linux package has a personal caretaker, who users contact when they experience problems or when they have discovered a bug. This mode of operation knows no guarantees, but has, nevertheless, been highly successful.
A team of researchers at the University of Wisconsin compared various UNIX flavors by feeding random input into various tools such as diff, ftp, mail, etc. In the original study in 1990, as well as in a repeat study in 1995, the GNU and Linux software proved superior to its commercial competitors. The results of both studies were published in a curiously amusing paper Miller et al. (1995).