The Opera desktop team has released Opera 25 developer stream and is available to download for Windows, Mac and Linux user. This version has added support for Web Notifications. Mac version has got Network installer, which Windows version already has. Don’t worry, Opera is still offering an offline package for Mac.
"From now on, Opera officially supports web notifications. These are a special kind of pop-up triggered by a site. Notifications alert the user outside of the context of the browser. Usually, the operating system UI is used to display the alert. This is very convenient way for web page and web app makers to inform their users about events, such as the delivery of email or a comment posted on a blog". said Przemek Kudła in Opera blog.
Testing Web Notification in Opera
To test web notifications in Opera developer, if you’re using Gmail, enable desktop notifications for it by visiting the settings, and whenever you receive a new email or chat message web notification will appear on your desktop.
You can check the full changelog for this version here.