Don’t be fooled by the rosy citrus hue; this is an unparalleled bitter flavor. Campari is de rigueur in drinks that call for this ingredient, but Gran Classico and Luxardo Bitter are nearly as popular.
Aperol is a similar type of Italian bitter, but is much sweeter; you’ll find it listed as “Sweet orange apéritif” instead. If you’re flexible on bitterness or sweetness, you can typically use either one in most drinks that call for one or the other. Cappalletti is right in the middle between the two types – it’s as sweet as Aperol, and as bitter as Campari.