Any good third party packages for line by line focusing that work across all major modes?

Be more specific. Is this functionality you use in another tool? If so, give that as an example or search for "Emacs + name of tool".

Emacs has a really cool feature called narrowing its not line by line but you can narrow a buffer to only show a function or highlighted region which is really great for focusing for me.

Yeah, me too. I love narrowing.

How?

No, just GNU emacs, no other external tools

It doesn't want to work on GNU GTK emacs, am I doing something wrong? `m-x narrow-to-page RET y`

Not totally sure how narrow-to-page works or defines a page. I usually use narrow-to-region or narrow-to-defun

I think I like `narrow-to-region` better.

Straight from the emacs manual: >Within some text files, text is divided into pages delimited by the formfeed character (ASCII code 12, also denoted as ‘control-L’).

What does line by line focusing mean to you? If you describe how it is supposed work people can help to achieve it in Emacs.

Not sure exactly what you're asking for, but see if hl-line-mode does what you want. I like it when I need to navigate in lots of dense data and want to keep my visual focus on one line at a time easily. Works on any major mode.

Is it on MELPA or will I have to install an .el?

I think it's in the default install of the latest emacs.

Okay, thanks!