For those coming from a Windows environment are keen to the small window previews for running apps, ChromeOS has this option, too. It just has to be enabled.
To enable it…
Open up the Chrome browser and type the following into the address bar:
Once enabled, you’ll need to restart the ChromeOS device for it to take full effect. The browser will give you an option to ‘Restart,’ but this doesn’t always work. You’ll want to take the extra effort and restart the ChromeOS device manually.
Now, when you hover over the icon of a running app on the ChomeOS Shelf, it will display the running instance.