"Mac users will be happy to know that rich notifications are being implemented on Mac. It's still under heavy development but you can play with them by running chrome with the --enable-rich-notifications switch (no flag yet)", said Beaufort.
TNW notes that Chrome OS notification center was previously ported to Chromium and then to Chrome Canary but only for Windows. Now that it's coming to Mac that paves the way for Google Now.
As for Google Now, the feature is still limited to Chrome OS and Windows, and even then it’s not exactly accessible: the Google Now server URL is still a secret (if you know it, you can set localStorage['server_url'] to the correct value and have a look around). The intelligent personal assistant, currently only officially released for Android and iOS, can be turned on via a flag at the very bottom of the list in Google’s Windows browser (last we checked, the flag is also there in Chrome Canary for Mac, but still says “Sorry, this experiment is not available on your platform”).
Google Now was recently released for iOS via the Google Search app.