Zengin System
Japan's national interbank transfer system, running since 1973 and as dependable as it is dull – almost always.
The Zengin Data Telecommunication System went live in 1973 and connects virtually every Japanese bank, credit association and agricultural cooperative. Since 2010 it has been operated by the Japanese Banks' Payment Clearing Network, Zengin-Net. Salaries, invoices and person-to-person transfers all run through it, and its fixed-length record layout is so entrenched that it's simply known as the Zengin format. In October 2018 the system went 24/7, and the same year brought ZEDI, an ISO 20022-based channel for richer remittance data.
It had run for nearly fifty years without serious incident when a relay server replacement in October 2023 stalled transfers at around a dozen banks for two days. Millions of payments got stuck, which in Japan made national news on roughly the scale of a late Shinkansen.