Use jQuery actions on scroll, for example to show a header only on scrolling up, or changing section color when scrolling past a specific element.
Check with JS if the URL that the visitor came from when landing contains a certain string
Create a select-like behavior from a radio or checkboxes list by making the list appear only on hover, like a sub-menu.
Induce custom post behavior with the default WP posts by changing the labels. Combine with ACF to create more custom post behavior.