From a high level, Gmail and Outlook might seem like competitors to each other. They're both pieces of an email system, but there are vital differences to understand. Gmail is a web app that's powered by Google, but access is offered to desktop clients through Google's Gmail API. When apps want to sync data from Gmail or Google Calendar, they prompt the user the login through the Gmail API, and the user doesn't have to give the new app their password information as Google hands the app a token to access the data. Gmail offers @gmail.com email addresses for free.