from streams session

end-of-stream - specify a callback to be called when a stream ends (which is surpsingly hard to get right)
duplexify - compose a Duplex stream from a Readable and a Writable stream
pump - pipe streams together and close all of them if one of them closes
pumpify - combine an array of streams into a single duplex stream using pump and duplexify
through2 - tools for making Transform streams
from2 - tools for making Readable streams

from "participatory modules" session

create-module create a simple module skeleton in a new directory
standard - a no-bikeshedding code standard
- useful for participation especially when added to CI and tied into pull requests because it's much less personal when an automated service tells you to change the way your code looks than when a maintainer does
istanbul - code coverage
- new contributors can help by increasing test coverage
nyc - code coverage that works with subprocesses
lab - test runner used in hapi
collaborator - add collaborators to github & npm, get a contributors.md
documentation.js - write docs in JSDoc format, get html/markdown/dash output
- provides a framework (JSDoc) for new contributors to help with documentation
semantic-release - automate semantic versioning
- takes the pain out of figuring out what a breaking change is (which can help if figuring out if a pull request is a major/minor change for example)
standard-readme, see also - a nascent module for linting your readme
- parts of a good readme include examples and contribution guidelines
pull-me-tender - do you have pull requests?
- quicker feedback on pull requests keeps up momentum/motivation of new contributors

other "participation hacks" from that session included:

a CONTRIBUTING.md that lays out how to participate, whether the maintainers have time and desire to specifically help new programmers or people from marginalized groups, etc.
"open open source" distributes ownership (and ownership can increase motivation)
"help wanted" labels for new contributors help contributors find good pieces for a first contribution
smilies/emoji/links to process documentation can help new contributors not get scared away by tone of critical feedback ("please rebase this." vs. "almost there, just needs a rebase first :)")