When you look at the bottom of your GMail window, you'll notice links in the footer, cycling through more or less helpful tips as well as Google advertisements.
For years now, one of these links has been to the GMail Notifier for Mac:
Sadly though, this link to http://mail.google.com/mail/help/notifier/index.html (forwards to http://toolbar.google.com/gmail-helper) has, also for a long, long time now, been a not found error. As you can't open a bug report with Google, I've emailed the GMail service people about this before, but I guess dead links in production software are not on top of their todo list.
Ah well, maybe they google for "Gmail fail" sometimes and find the bug report this way ;)