A lot of the big, complicated systems that undergird our economy—banks, airlines, stuff like Social Security—still run on old-fashioned mainframes. There’s still a lot of COBOL code out here. Florian Mueller writes:

At the recent launch of its new mainframe generation — the biggest event of its kind in 20 years — Tom Rosamilia, IBM’s general manager for System z, was so exuberant that he forgot about antitrust and told a group of UK journalists the truth: “Western civilization runs on this system.”

What are some of the key population-scale government computing applications? Other than, e.g., NSA signal processing stuff, I mean. That’s sort of the obvious candidate, and it’s gotten plenty of press. What’s not obvious?