Calypso was released by Hopsteiner in the early 2010s, bred with an aroma profile that stands apart from most high-alpha American hops of its era — rather than the citrus, pine or tropical-fruit vocabulary that dominates that category, Calypso carries apple and pear notes alongside a milder citrus edge, a combination closer to orchard fruit than to anything typical of a hop this potent.
Calypso covers real bittering ground at 12-14% alpha acid, and like Glacier and Loral it was bred with low cohumulone in mind, meaning the bitterness it contributes at a given IBU reads smoother than an equivalent number from a higher-cohumulone high-alpha hop. Its orchard-fruit aroma is distinctive enough that many recipes use at least part of the charge for late-boil or dry-hop purposes despite its bittering strength.
Nugget is a reasonable substitute for the bittering role given a comparable alpha range, though it lacks Calypso's specific apple-pear character entirely. Palisade offers a partial aromatic substitute given its own stone-fruit lean, though the match isn't close. American pale ale and IPA both use Calypso where a smoother, less citrus-dominant fruit character is the goal. The low-cohumulone quality won't show up in a raw IBU number from the calculator, only in the glass — but the calculator still gets the weight right before that quality has a chance to matter.