The O.G. API framework
Express.js is a really neat and highly adopted framework for Node.js that makes it trivial to build an API. It's by far the most popular one due to it being created near Node.js' time of creation and how much support the community has poured into it. Express is synomous with Django for Python, Sinatra for Ruby, Spring for Java, and Gin for Go Lang
Other options
There are many other frameworks, some faster, some newer. Many of them have been inspired by or even built on top of Express.js. It's also the one I know the most about 😄.