Four years ago, Google introduced the idea of Chrome apps. These were web apps that would work as if they were native apps with offline capabilities. However, Google recently announced it would no longer support Chrome apps because they are used by only 1% of Chrome users.
The idea of Chrome apps was mainly introduced to help Chrome OS feel more like a real operating system. You could continue using Chrome apps even when you were disconnected from the Internet. Your changes would be saved locally, and then, if needed, they'd be synced to the web service as well.
Chrome apps also had other capabilities that regular apps or browser extensions didn’t have, such as more direct access to system hardware (USB, Bluetooth, cameras, etc). You could also use the Chrome app outside of of the Chrome browser, as if it was a standalone application.
Google even worked on helping developers port existing C++ applications to Chrome through the Native Client sandboxing technology. Google didn’t specifically address Native Client apps in its latest announcement, but with Chrome apps being deprecated soon, and with Android native apps also coming to Chrome OS, supporting Native Client apps may not make much sense in the future. Multiple browser vendors are also working on a standardized alternative to Native Client, called WebAssembly, which may help speed up the demise of Native Client support in Chrome as well.
Starting in late 2016, new Chrome apps will only be shown in Chrome OS. Existing apps will work in the Chrome browser on all the desktop platforms until the second half of 2017. In early 2018, only Chrome OS will be able to load Chrome apps. It’s possible that many enterprise and institutional customers of Chromebooks are already depending on some Chrome apps, so Google will probably support them on Chrome OS for a few more years.
Developers of Chrome apps, such as Open WhisperSystems with its Signal for Desktop client, will have to either transition to a similar solution, such as Electron or NW.js, or give up on the “native” web app idea completely and write regular native applications instead.