I haven't studied the guts of it, but I've been impressed recently with Github. It feels like a normal, page-by-page application, with human-readable URLs, and none of the usual SPA shenanigans as far as after-page loading, infinite-scroll nonsense, or broken back button behaviour... but then stuff happens like a page that's sitting open on a PR automatically pulls new comments as they are posted, and it looks identical to if that page was loaded afresh. Spiffy.