If you're up for it, you can add your own bank/creditcard company/whatever as a plugin to it - I think the examples there are decent. I could also help if need be!
Many US banks support OFX (though they may call it QFX, DirectConnect, or simply advertise Quicken support). The OFX spec is a bit of a pain, but there are a number of open-source libraries to query/parse it. I wrote one in Go: https://github.com/aclindsa/ofxgo
ledger-reconciler uses headless chrome underneath to screen-scrape all its information from banking/creditcard websites. That's how all the plugins hook into it.
It does not use any public or private banking APIs.
Transaction pull can be done in GNUCash with aqbanking. It's not fully automated, as it's a GUI and there's a manual review step. And also the aqbanking interface is terribad.