Recently I posted this: Categories in a quadrant.
As the quickest description I used a graphics program to show what it would look like.
It seems to me that logically this could be achieved with a grid of some sort. I've used grids before with html and ccs but that was with text (paragraphs) and images to arrange-in-order for smaller screens. I have a couple of test forums on the server and even did a quick 50% width and float-left on one forum and while that was encouraging there are of course the templates in phpBB which have always been a bit maze-like for me.
KevC posted the link to your your Project Durango and while it's in that ballpark there were too many modules for me. I downloaded it and while looking through the maze I was wary that in some coding corner I would turn and be confronted by the phpBB Minotaur.
Best I can tell it's identifying (in my case) the category and subforums below it in each one. Is that a grid in use or something else due to the configuration of phpBB?
Anyway, I hope I explained that correctly. Any suggestions appreciated.
Thank you
Daniel