MT940
Swift's text-based bank statement, read by accounting systems for decades and slated for replacement by camt.053.
The message is a series of colon-delimited tags: :25: for the account, :60F: for the opening balance, one :61: per booked entry and :62F: for the closing balance. Its sibling MT942 reports intraday, and MT950 is the bank-to-bank variant. The format was designed for the Swift network, but plenty of banks, particularly in Germany and the Netherlands, also offered it as a download in online banking.
The weak spot is field :86:, information to the account owner. It is free text, six lines of 65 characters, and every bank stuffed references, names and fees into it according to its own conventions. An MT940 reconciliation routine was therefore really one parser per bank. The format lives on in a lot of corporate integrations, because it works and nobody wants to touch it.