Most services I use integrate Plaid. I believe Plaid is just a federated authentication glue that accesses your bank's systems and is granted access to account balances and ACH details (routing/bank account numbers).

It always struck me as an odd product, since I can just plug my ACH info in directly, but it does provide some level of convenience by allowing, say, a roboadviser app to show the embedded balances of my other accounts.