It is great to see Mithril again on front page of HN, it is one of the most simplest and easiest modern JS frameworks. I only know flarum [0] as a project which has used Mithril mixed with jQuery [1] and personally, I am quite amazed how snappy it is.
Aside, Flarum's scrubber/scrollbar is brilliant and a massive upgrade to how you have to navigate a traditional message board like phpbb where you kinda guess at arbitrary pagination til you're where you want to be.
Good example of using a SPA to improve UX of a "document-based" app.
Another example of this sort of SPA improvement is when clicking on a list-view item brings up an overlaying modal of the item-detail page which is nicer when user is browsing rapidly.
There's also https://flems.io a snappy web playground with an open source embeddable core[2] ( shameless self promotion :P )
[0]: https://github.com/veloce/lichobile
[1]: http://lichess.org
[2]: https://github.com/porsager/flems