I come across so many great tools by accident, gitignore.io for - TopicsExpress

I come across so many great tools by accident, gitignore.io for instance I came across when looking for documentation on .gitignore and today I came across gistboxapp/, which allows you to save any code you come across on the web as a gist. I feel like theres likely a lot more tools Im missing out on, what are some other indispensable tools that I should be using? Edit: I threw together a google form for a gistbox group, Ill add whoever wants in https://docs.google/forms/d/14QcIGGS_mBRHovviNcUY6a4OLehUWNWxy5GX1PfRobU/viewform