How to keep track of programs that I've installed from the terminal?

I'm learning front-end web development. This is my third month. So far, I've installed so many apps from my terminal until I can't keep up with how many apps I've installed. These apps are ruby on rails, node-sass, some npm apps, and many more. The problem is that I can't see these apps in my application folder (I'm using mac). Where can I locate these apps? How can I keep track of them? and how can I uninstall them? Thanks