semver.io
A webservice for tracking versions of Node.js and npm
semver.io is was a plaintext and JSON webservice that tracks all available versions of Node.js and uses that information to resolve semver range queries. It's used by Heroku's Node.js buildpack and is open-sourced on GitHub. Community members have contributed semver-as-a-service support for other projects like npm, iojs, nginx, and MongoDB.