Recs.
Updated
Open source Node.js framework built on top of Express optimized for building APIs for mobile, web, and other devices. Connect to multiple data sources, write business logic in Node.js, glue on top of your existing services and data, connect using JS, iOS & Android SDKs. There's also a Client SDK for Android, iOS and the browser (using Angular). Loopback's Juggler component can connect to MySQL, Oracle and Postgres and addition to MongoDB.
Specs
Pros
Pro Schema Discovery
Standard first-tier ORMs allow record/table/model/schema CRUD, but the developer must know the model and specify beforehand. Loopback allows a developer to connect to an unknown schema and Loopback constructs the JavaScript object representation of discovered records/tables/models/schema.
Pro Supports Migrations
Has support either auto or explicit migrations, but I believe the are generated from the models and sync'd to the database. https://loopback.io/doc/en/lb4/Database-migrations.html
Pro Support for TypeScript
Here's an example of a model definition using attributes on top of a TypeScript class definition: https://github.com/strongloop/loopback4-example-shopping/blob/master/packages/shopping/src/models/product.model.ts
Cons
Con StrongLoop owned by IBM
StrongLoop is the main contributing organization for Loopback, and it was purchased by IBM. Now many people fear quality decline or license change is in the future. On the bright side, they seem to be developing complimentary tooling, but this may result in expenses or lock-in down the road.