And ADABAS (officially declared fully supported through the year 2050 and beyond). Most often considered non-relational too.
High-value transactional environments most often neither relational nor even running on operating system (in modern sense at least), like zTPF "because a real operating system is too high level and therefore too slow for real transaction processing needs". Current users of TPF include Sabre, VISA, American Airlines, American Express, HP SHARES (formerly EDS), Holiday Inn, Alitalia, KLM, Amtrak, Marriott International, Travelport, Citibank, Citifinancial, Air Canada, Delta Air Lines, Japan Airlines and many others.
High-value transactional environments most often neither relational nor even running on operating system (in modern sense at least), like zTPF "because a real operating system is too high level and therefore too slow for real transaction processing needs". Current users of TPF include Sabre, VISA, American Airlines, American Express, HP SHARES (formerly EDS), Holiday Inn, Alitalia, KLM, Amtrak, Marriott International, Travelport, Citibank, Citifinancial, Air Canada, Delta Air Lines, Japan Airlines and many others.