For Windows, I am surprised no one has mentioned TextPad.

It has the usual libraries that makes colors for various types of code. You can also create your own color scheme if you have a more obscure need.

You can search & replace using regular expressions. You can search and mark each line where it found an occurrence, and then act upon the marked lines. It saves about a dozen of your recent search strings and replace strings for quick reuse.

It comes with some predefined snippets of code that you doubleclick to insert into the current document (examples are html code and ANSI codes). You can also save your own code snippets if you have some that you use all the time.

You can select multiple areas in a single copy operation. You can turn on "block" select mode, which lets you select any square of text anywhere (handy when you want to delete a whole column of data that runs vertically down a file).

You can record macros.

I sound like a commercial for this software! Honestly, I don't work for TextPad, I'm just a loyal user!