Unfortunately there is no true common app that really puts you in front of all YC companies yet. Because TripleByte charges companies a fee for each person hir

Unfortunately there is no true common app that really puts you in front of all YC companies yet. Because TripleByte charges companies a fee for each person hired, not all YC companies work with them. And because Work At A Startup is so new, not all YC companies are using it yet. You'll get the most reach by using both.