For me it was a free email account when you had to be invited for gmail. Then I got an Android phone and used the account for it. Then I used the calendar app

For me it was a free email account when you had to be invited for gmail. Then I got an Android phone and used the account for it. Then I used the calendar app which used the same account. So it vendor lock-in all the way. But I already migrated my email to a VPS and will migrate my calendar and contacts as well. But this is not something everybody knows how to do.