From the folks at Basecamp comes Turbo:
Nice, but that “without requiring you to change your server-side generated HTML” part is not exactly true though, as you have to sprinkle some
turbo-* custom elements and
data-turbo-* attributes all over your markup. Once those are in place Turbo will do its thing and progressively enhance the experience.
If you want to do more than the features provided by Turbo you can bundle it up with Stimulus and Strada. All three together are published under the name Hotwire.