If you read the title of this post and didn't really understand what it was about until you saw the screenshot, you're not alone. Most of us on the team had to do a double check when we caught the news because we didn't immediately recall what this web notification widget really was. But now that we do, we're heartbroken about the news... not!
The widget showed up when you tapped that bell icon near your avatar image in the toolbar of any Google site. Despite its interesting premise — a place for all your Google notifications — it was never picked up even inside the company. Only Google+ (RIP), Google Photos, and Hangouts Chat used it. With the first one going away and the other two offering proper browser notifications, it made no sense to keep the widget alive.
The widget allowed Google+, Google Photos, and Hangouts Chat notifications.
The deadline is set for one month from now, March 7. Until then, you can ring that bell (icon) as many times as you please. But after that, it should die the same death as many of Google's other products and features.