They provide high availability, automatic restart, file watcher, runtime performance and resource consumption insights, and clustering.
PM2 is a production process manager for Node.js applications that has a built-in load balancer, enables you to keep applications alive forever, reloads them without downtime, helps you to manage application logging, monitoring, and clustering.
Forever is a simple command-line interface tool to ensure that a script runs continuously forever, simple interface makes it ideal for running smaller deployments of Node.js apps and scripts.
StrongLoop Process Manager (Strong-PM) is a production process manager for Node.js applications with built-in load balancing, monitoring, and multi-host deployment. Includes a CLI to build, package, and deploy Node.js applications to a local or remote system.
Nodemon is a utility that will monitor for any changes in your source and automatically restart your server. Perfect for development. Just use nodemon instead of node to run your code, and now your process will automatically restart when your code changes.