> Does anyone have examples to share of open source projects that have very low friction for drive-by contributions while still maintaining quality? Projects with very clear documentation and instructions for contributing?
Yes, absolutely. Read https://rfc.zeromq.org/spec:42/C4/.
We developed the C4 contract (in the form of an RFC) precisely to teach maintainers how to welcome new contributors while keeping quality high. It took many years to refine this approach. By formalizing it, it becomes really simple for projects to adopt: all you need in your README 'Contributing' section is a license (we recommend MPLv2), a link to this RFC, and later a style guide to ensure consistent code style.
The thing about C4 is that it teaches people to make small testable patches, and to trust new contributors. We know from experience that it's users of a project who keep it alive. Original authors and core maintainers burn out, get full time jobs, start new projects. As long as you have users, though, you have potential contributors.
Small patches, merged immediately, with reviews and improvements made asynchronously over time. This style is lovely to work with, kills bike shedding (we argue with new patches rather than comments), and reduces the friction in the project to as low as possible.
More on optimistic merging: http://hintjens.com/blog:106
In terms of friction: we aim to get a patch live on master within a few minutes. If that breaks master, we fix it either with a new patch, or a revert. Anyone can submit a patch, anyone can revert or improve previous patches. You can't merge your own pull requests. We work straight on master so new code is pushed aggressively towards users capable and willing to use it (those who build off master). We use CI heavily to test backwards compatibility, i.e. that existing APIs and protocols haven't broken.
There is also a whole theory of how incremental testable patches remove the need for "intelligent design" and thus the dependency on brilliant key individuals. That's another story which I cover in my book "Social Architecture". Free to read online if you want it.
Best of all, this process works. We know because we've been using it quietly and successfully in the ZeroMQ community for years.
Of all the things I've done in open source, I consider this my most important work, as it solves the really essential problem raised in TFA, which is how to keep open source projects alive over the long term.