Fonts and typography are fun. Material Design is a framework (developed by Google) that basically geeks out on how to assemble your typographical elements together into a design language. If you're into fonts and typography, it's fantastic. It provides a theming engine, reusable components, and can pull different user interfaces together under a common design paradigm. I'd highly recommend looking into Borries Schwesinger's book "The Form Book" if you're going to be working with Material UI or are otherwise new to component design.
We wanted a JSON datastore that could save the state of our bioinformatics visualizations without destructive normalization. As a leading NoSQL data storage technology, MongoDB has been a perfect fit for our needs. Plus it's open source, and has an enterprise SLA scale-out path, with support of hosted solutions like Atlas. Mongo has been an absolute champ. So much so that SQL and Oracle have begun shipping JSON column types as a new feature for their databases. And when Fast Healthcare Interoperability Resources (FHIR) announced support for JSON, we basically had our FHIR datalake technology.
We use Mocha for our FDA verification testing. It's integrated into Meteor, our upstream web application framework. We like how battle tested it is, its' syntax, its' options of reporters, and countless other features. Most everybody can agree on mocha, and that gets us half-way through our FDA verification and validation (V&V) testing strategy.
We mostly use rollup to publish package onto NPM. For most all other use cases, we use the Meteor build tool (probably 99% of the time) for publishing packages. If you're using Node on FHIR you probably won't need to know rollup, unless you are somehow working on helping us publish front end user interface components using FHIR. That being said, we have been migrating away from Atmosphere package manager towards NPM. As we continue to migrate away, we may publish other NPM packages using rollup.