This is a difficult one. It's easy to point to codebases that indeed have been maintained for many years - but that doesn't mean they were designed well. Look

This is a difficult one. It's easy to point to codebases that indeed have been maintained for many years - but that doesn't mean they were designed well. Look at a project like SVGEdit. It's by far and away the most popular open source project for in-browser SVG manipulation. It is the "most maintained" repository for any software in its niche. It is also a five thousand line blob of jQuery code. That's an extreme example, but the point is: a project could become beacons for OSS development not because it is amenable to change, but because it is a very useful or prominent tool.