In addition things other people have mentioned, like magit, I would add org-capture as a good example. Let's say I'm busy at work in a buffer and a thought com

In addition things other people have mentioned, like magit, I would add org-capture as a good example. Let's say I'm busy at work in a buffer and a thought comes to mind: "I could refactor that other module using this code". Instead of doing it immediately and breaking my flow, I press C-c c, select "todo", type "refactor that other module", perhaps add a tag, a category etc. then C-c C-c and it's filed away. What's really important about all of this is, it's all Emacs. Every magit buffer, every org-capture buffer, it's all just Emacs buffers and they're all configured the way you like. If you need to do a regexp find and replace while you're capturing a note, you can. If you make a typo in a note, in a commit message, in an email or anything else, it's spell checked and you can correct it with the same key you always do. This integration is the real magic.