Not a format, a website; arxiv.org.

You wrote: "I can read papers from 12 different journals and they're all in the same format there."

Suggesting some file format, or perhaps presentation format.

ArXiV files are downloaded in either .PDF or maybe .HTML. In my subfield (computer vision), most of the action happens in actual journals/conferences for now, so when authors submit to ArXiV, they submit .PDFs because the work usually was also intended to appear somewhere else.

ArXiV does not specify a style guide so you get this weird mix of IEEE/PAMI/single-column/double-column, but that's not really a detrement to its readability since journals wouldn't usually pick an unreadable style anyway.

Thanks, though I'll note you weren't who I was asking the question of ;-)

I figured the format was likely "academic articles, mostly prepared with LaTeX, published as PDFs", but the commenter was being less than clear, even on reiteration.