Kudos to SurveyMonkey for their very clear, user-friendly sign up form (pictured above) that lets you sign up with your existing Google, Facebook,or Microsoft credentials. They’re far from the only SaaS using these Single Sign On (SSO) solutions, but they’re doing it really well. Trello comes to mind as another very smooth SSO implementation.
With SaaS proliferation comes nontrivial administrative overhead, and SSO is one of the main ways to keep things under control. Highly recommended for all these organizations already using GSuite or O365.