There sure is!

Here's the introductory post, explaining how you can download or link Observable notebooks as ES modules, and use the open-source runtime to evaluate notebooks or just render specific cells: https://beta.observablehq.com/@jashkenas/downloading-and-emb...

Here's an example of a toy notebook being embedded on another domain: http://ashkenas.com/breakout/

Finally, because Observable notebooks are of course, themselves, web pages, here's an example of a notebook embedding itself: https://beta.observablehq.com/@jashkenas/ouroboros-a-noteboo...