A tool I haven’t quite seen mentioned here yet that I’m loving is bash-it. It’s like oh-my-zsh for bash. It gives you a huge amount of plugins, aliases, and themes to increase your bash productivity without spending a bunch of time doing manual configuration.
Also, the redux devtools extensions. I’ve been doing most of my frontend work in react/redux lately and having a tool to show you all your state mutations as they happen makes debugging a delight.
And for anyone on OSX, quiver is a seriously awesome note-taking app with built-in markdown and code snippet support.