Chrome: If you have a bunch of Gmail accounts you might grow sick of switching between them using the native switch account feature. Google Mail Multi-Account Checker is a Chrome extension that notifies you and switches between new emails in up to nine accounts.
The extension sits in your toolbar with the number of unread emails. Clicking on it will show you all the newest emails you’ve received in each of your accounts. You also get notified of new emails to any of the accounts. There’s an option to enter in all your login credentials as well, but the developer notes your credentials are stored as a plain text document, so you might not want to use that feature if you’re sharing your computer. It’s a great way to keep track of multiple Gmail accounts without having a bunch of tabs open at once.