I've been using some of these "opensource" tools for years now, there might be better tools so do comment below what your day to day tool is that helps you with work.
Screenshots: We take screenshots daily and share them on twitter, dev.to, slack and sometimes even in an email 👨💻. For that reason and easy to share I use Skitch. It is super easy to take a screenshot, make some pointers hit (copy) and (paste) and off to next task.
CheatSheet: This is one of those tools that I really love having on my Mac, sure I could be a Guru in some apps, but VI,VIM there is no Guru, there are Novice users and Advanced users. CheatSheet basically gives you supportive cheatsheet commands you can use with most tools like Sublime, VI, Mail, Chrome and many many more.
Alfred: I use Alfred quite a bit compare to Spotlight (I think this one is for Mac users only). Alfred basically helps me search my Mac in more advanced form + with the workflows you can add github, and many other helpful search functions.
Terminal on Steroids: Oh My Zsh! seriously since I started using it (last year) I fell in love it it so much.
Here is why...
I work on Kubernetes on daily basis and switch between namespaces, clusters quite a bit. That said, its really nice to have a visual representation which namespace and or cluster you are on while also giving you pointer that you are on blabla-patch1 branch in github. If you are on any type of terminal don't skip on Oh My Zsh!
What are some of your day to day must tools that did not come with your laptop installed?