Google Assistant smart displays are (in their current form) smart speakers with some level of visual feedback. Asking for the weather shows you the forecast for the week, asking for the news can show a video news briefing, and so on. There are only a handful of interactive smart display experiences right now (like step-by-step cooking), but now Google is giving developers the tools they need to create them.
One interesting aspect is that these experiences won't just be for smart displays — they'll work on Android devices as well. Google says Interactive Canvas is already available for building games, and the company will be adding more categories soon.