In the Czech Republic, it's pay slips/bank statements, or a work contract for mortgage (you cannot fire someone without a reason). There is a central government database of people who didn't pay a debt on time.
In Germany, also pay slips and work contracts. Additionally, there is a semi-private government-mandated company (I never understood why Germans don't complain about this) that maintains a database of existing debtors. You basically start with a perfect score and it decreases only when you don't repay on time.
There is a gigantic difference between who can get mortgages and at what kind of leverage one can get in Europe vs. United States.
Completely private and manual underwriting exists and always existed in the United States. The reason that it is not popular is that the vast majority of Americans would not qualify under any private underwriting guidelines for most of the loans Americans get ( and successfully pay for ).
In Germany, also pay slips and work contracts. Additionally, there is a semi-private government-mandated company (I never understood why Germans don't complain about this) that maintains a database of existing debtors. You basically start with a perfect score and it decreases only when you don't repay on time.