Ask HN: Software to edit code in many vertical strips?

I have a large monitor. I want to see a ton of code at the same time - instead of a single vertical scroll of code, I want lots and lots of narrow vertical columns of the same file shown side by side.

A big use for this is code reviews, so even a non-editable view of text/PDF would be okay. Editable would be even better.

I used to have some software back in the early 2000's, when Mac OS X was new that did a read only view in this way, but I can't remember the name.

Any suggestions for me?