The brain is a library that makes the user to easily create neural networks and then train them depending on input/output data. As training takes up a lot of resources, it is better to run the library in a Node.js location, though a CDN browser version can also be loaded directly onto a web page. There is a small demo on their website that can be trained to identify color contrast.
It is the most vigorously maintained project on the list, Synaptic is a Node.js and browser library that is architecture-agnostic, allowing the developers to build any type of neural network they want. It has some narrow built-in architectures, making it likely to test and relate different machine learning algorithms. It also features a well-published introduction to neural networks, a number of practical demos, and many other great tutorials illustrating how machine learning works.