Web Crawler
This is my current project. I’m endeavoring to crawl 1 billion web pages for a couple hundred dollars. It is ~80% done.

Build Your Own Regex Engine
Build a simple regular expression engine in less than 40 lines of code.

React Column Layout | npm package
A column based layout system (think Pinterest style) that works responsively without special configuration.

Other Major Open Source Contributions

The popular Nodejs ORM.