The answer I got from an IRC channel:
Sequelize is an ORM that includes some query builder stuff; Knex is just a query builder, not an ORM.
ORMs don't actually fit very well in many use cases, it's easy to run up against the limits of what they can express, and end up needing to break your way out of them.
But that doesn't really explain the pros and cons of each. I am looking for an explanation, and possibly a simple example (use case) highlighting those similarities / differences.
Why would one use one over the other?