I noticed something curious when I booted my first project atop Rails 5 in development mode: that when the development server was idling, the title bar on Terminal.app would read “fsevent_watch”.

On further investigation I found this pull request and this posting to the official Rails blog. With this pull request, Rails got a new event-based filesystem monitor. Whereas previously, both class reloading and asset recompilation were governed by a walk of the project tree reading mtimes off of files, with Rails 5 we finally have a more enlightened, push-like model based upon file system events. For large projects,  the effect on the development experience is immense. Though this feature slipped in pretty stealthily, I feel that for practical purposes it is probably one of the most important and impactful changes in the framework’s history. Give it a try by updating to Rails 5.0.0 or higher.