Utilities are the tools anyone might use, as opposed to dev tools, which are the tools developers use: a calculator, a unit converter, a world clock, a password checker, a QR generator, a printable calendar. Most of them are a weekend's work by one person, and most of them are exactly the kind of site the town was built for — many side projects, one square each.
It is a young district. The taxonomy grew this slug when the classifier kept filing calculators under dev tools, and the sites are still moving in. Newest-first is the order to watch.
A utility with no favicon is a clown in town until it adds one; the Hall of Clowns explains, and the fix takes five minutes.