I guess it's not popular or all that well-known anymore, but for quite a while there's been a Quicken-led banking interface for some banks. Known as OFX or Direct Connect, it provides at least one-way (download) access to banking transactions. I think there's a way to upload as well but have never used it nor had a bank that supports it for upload.
My bank has a separate enrollment - it was free - offering download-only access to my transactions. I haven't used it in awhile (just too much on my plate) but it worked well as recently as 2016.
My bank has a separate enrollment - it was free - offering download-only access to my transactions. I haven't used it in awhile (just too much on my plate) but it worked well as recently as 2016.
https://github.com/aqbanking/aqbanking is one open implementation for the interface.