Express.js is the workhorse of the Cloudcraft.co backend. It's not the most exciting part of a stack, but it works, is very well documented, and you can find a plugin for almost everything you could possibly want. We also carefully evaluated Koa.js, but decided not to go down this route: fewer plugins, less documentation & answers online. I'm also not personally convinced by the generators yield syntax at all. ES7 async functions looks like a much better bet, and with Promises and Babel I can have that already today.

I use express.js for nightly.zerotoherojs.com and dojo.zerotoherojs.com web apps.

Express is well-known, lightweight, works out-of-the-box, has great middleware support and has minimal learning curve.

It is the best framework to start developing a general Node.js web app.

I use Flask for times when I need to create a REST API that interfaces with other Python code, or there is no specific reason why I'd want to use Node.JS. I prefer Flask because of its small learning curve, allowing me to get started coding as quickly as possible

This lightweight web framework enables quick REST API development while enabling easy clustering, and the usage of multiple worker processes required to scale the REST API service to meet high volume requirements.

I'm fluent in ExpressJS, but over the past two years I have moved to HapiJS. Similar results, but I find Hapi to be more full-featured towards my app, api and service needs. I can operate confidently in both.

PrometheanTV utilizes the ExpressJS web application framework to deploy various web applications and services including the Broadcast Center Tool, our video embed service, and our REST API.

We rely on ExpressJS to serve our content simply, easily, and effectively, without the bloat-ware. Big thanks to StrongLoop for supporting this package.

Service to query NOAA weather forecasts data and service to build tidal current forecast maps using AWS EC2 and Geoserver

Flask drives our APIs, both the Website APIs and the majority of the REST Messaging APIs

used flask for a few personal projects. enjoyed its simplicity and ease of use.