I definitely suggest sublime text, that's cross platform. It's nice to have all the colours, it's most ppl's favourite of those i've spoken to
Atom: An open source text editor. Light Table: A stylish text editor. Bluefish: A superb cross-platform editor. Vim: A powerful tool.
Having used Sublime Text and Atom.io for years on OS X. I came to realize that Microsoft Visual Studio Code is much more powerful than any of those, and it's free. I still keep Atom as default for previewing files because it loads up lightning fast, but if I do more than just a few edits VSCode has too much to offer, starting with its debugging tools etc. ps. Also Vim is a powerful tool for working with multiple files and data from the command line. It will always be the greatest text editor.
I agree with everyone above who said Textwrangler. It's probably the best free option available. Paid Application-wise though, there's an app called BBEdit (I believe it's by the same people who made Textwrangler).
If you are looking for some IDE functions like code completion Coderunner is also nice, it does cost some money tho.
+1 for TextWrangler, I've been very happy with it over the past years, wouldn't change it for anything else.