DuckDuckGo Zero-click Info includes topic summaries, categories, disambiguation, official sites, !bang redirects, definitions and more. You can use this API for many things, e.g. define people, places, things, words and concepts; provides direct links to other services (via !bang syntax); list related topics; and gives official sites when available.
An API for interesting facts about numbers. Provides trivia, math, date, and year facts about numbers. For example, "5 is the number of platonic solids", "42 is the number of little squares forming the left side trail of Microsoft's Windows 98 logo", "February 27th is the day in 1964 that the government of Italy asks for help to keep the Leaning Tower of Pisa from toppling over"