TogetherJS is a free, open source JavaScript library by Mozilla Labs that adds collaboration features and tools to your website. By adding TogetherJS to your site, users can help each other out in real time.

I was the lead designer for the product and marketing materials, and I handled significant front-end UI work and prototyping. The tool saw massive adoption, with hundreds of thousands of sessions created and integrations into platforms like JSFiddle, Trello, and Mozilla Thimble.