Back in May, Google began launching rich notifications to the Chrome beta channel. Today, the update is rolling out to all Chrome users.
The new system will allow web developers to create sophisticated notifications that will pop up in the lower corner of your screen. You can dismiss them or take action directly from the box itself.
The feature is currently available for Windows users with a Mac update coming soon. If you want to disable only some of the notifications, you can turn them off on a source-by-source basis under Settings.
Richer notifications now available to all Chrome users [Google Chrome Blog]