Square / Block

Square, now under Block Inc, generates $21B in revenue—40% more than Stripe—making it the largest fintech conglomerate on this list. Cash App alone has 57 million monthly active users, processing over 1 billion transactions per quarter. CEO Jack Dorsey's $500M Bitcoin treasury underscores Block's crypto-first strategy, while the $29B acquisition of Afterpay cemented its BNPL dominance. Square's Clover POS system competes directly with Fiserv's Clover, but its unified merchant and consumer ecosystem sets it apart.