Can the menu system used here be shared?
 

I really like (and could use) the way the Tabs here link to different groups of forums. I know ther is a mod that does something similar using AJAX, but how is it done here, if it's not proprietary?

It's custom built but then so are most mods :), search for tabbed or tabs and you'll find what you want, there's one here https://vborg.vbsupport.ru/showthread.php?t=233135, you can either adapt it to look like here (but this is vb3) or ask the developer and see if they are willing to do it, there's also tutorials here, use the search again and search for "New tabs" in articles, here's a quick and easy one https://vborg.vbsupport.ru/showthread.php?t=271740