PM2 is described as 'Advanced process manager for production Node.js applications. Load balancer, logs facility, startup script, micro service management, at a glance'. There are four alternatives to PM2 for Linux, Self-Hosted solutions, BSD and Mac. The best alternative is Supervisor, which is both free and Open Source. Other great apps like PM2 are Phusion Passenger (Freemium), Reflex (Free, Open Source) and nodemon (Free, Open Source).
Reflex is a small tool to watch a directory and rerun a command when certain files change. It's great for automatically running compile/lint/test tasks and for reloading your application when the code changes.
nodemon is a tool that helps develop node.js based applications by automatically restarting the node application when file changes in the directory are detected. nodemon does not require any additional changes to your code or method of development.