Are Chrome web apps opened as a Windows executable file?
Yes, they can be opened like Windows apps, but they are not true Windows executables. Instead, they are essentially either special web shortcuts, or in effect, an application which uses Chrome as a virtual environment. In other words, these applications will not run on a computer without Chrome, and they will run on other systems (Mac, Linux) so long as Chrome is installed on them.
Thanks. Are they similar to apps for Chromebooks?
Yes, very much so.
There are two different types of installable web apps: packaged and hosted
A hosted app requires a .crx file that contains metadata describing the app. (The .crx file format is just a variation of ZIP that's used by Google Chrome.) An app's .crx file can be hosted on your own server or, more typically, by the Chrome Web Store.
You can easily make any existing web app installable, letting you publish it as a hosted app. There's no need to rewrite the web app or change technologies. All you need to provide are an icon and a manifest.
Thanks. Nicely put