We actually spent three or four years trying to avoid using ExpressJS, as it's more low-level than we would like. Our goal is to develop a modern tech stack that's productive for bioinformaticists, clinicians, and superpatients; and that means abstracting away from raw TCP and header management. We prefer most of those things to be already worked out, so we can save that mental effort for managing medical terminologies and ontologies. So, for a long time, we were using Meteor's DDP protocol instead of HTTP. It works great. But it's not widely supported. Eventually, we had another company volunteer some open-source code that sorted out the details of an Express based FHIR server implementation. So we were happy to pull it in since someone else was already managing it. Long story short, we include ExpressJS as a deep dependency in the Node FHIR Server Core library we use from Asymmetrik.
Most bioinformatics shops nowadays are hosting on AWS or Azure, since they have HIPAA tiers and offer enterprise SLA contracts. Meanwhile Heroku hasn't historically supported HIPAA. Rackspace and Google Cloud would be other hosting providers we would consider, but we just don't get requests for them. So, we mostly focus on AWS and Azure support.
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.