I've recently started working on my old side project which is this online jigsaw puzzle website. I did most of the development a few years ago, so it's not really using anything modern like web sockets and such. Anyways, here is the front page of the http://puzzle.massive.xyz which shows an image which you click on to start assembling that puzzle. The most recent puzzle that has had a piece move will be listed here.
When assembling the puzzle all the pieces that are moved will also move for any other players viewing that puzzle. It basically does a bit of polling every 15 seconds to check for other player piece movements. While I could set it to have the piece movements be more immediate, I found that having multiple players on a puzzle all moving pieces at once caused it hard to focus on the puzzle. So every 15 seconds it'll simply do a puzzle piece update which moves the pieces in a batch.
Oh, and the majority of puzzle images that I'm using are just random photos from https://unsplash.com. The Puzzle Massive site also has a simple form to upload your own images to create puzzles with up to 3000 pieces.
The design of the site is somewhat lacking. I'm more of a developer and not much of a designer. At the moment I'm just concentrating on a lot of the server side code to make it work better.
Check it out at: http://puzzle.massive.xyz