Symbolab is a search engine that searches for math and science content. Sure, you say, Google does that. But Symbolab searches for equations, formulas and expressions using mathematical symbols and scientific notations. And it can do full text searches as well. In other words, you can look for solutions, exercises and contextual information about a specific formula or you can look up information about, for example, quantum mechanics. Check out their home page for some sample searches.
KitchenPC is recipe search engine. Yep, there are other specialized tools out there that search for recipes (including Google's recipe search tool). KitchenPC not only searches a bunch of recipe sites to get the results, but you can also put in ingredients you already have and get matching recipes. Or tell it what ingredients to avoid. Narrow your search using a number of other options, such as skill level, diet, taste and time. Build menus and get a shopping list.
Ok, you are looking for some art, but you don't quite know who or what to look for. After all, you're not an Art History professor, right? You can search for specific artists, works, movements, techniques, or regions. Or if you don't have something specific in mind, you can use the browse feature. From your search results or when looking at specific works, Art.sy gives you tools and suggestions for narrowing the search or finding related works. They may not have all the works by specific artists, but you can also follow specific artists and get notified when new works are added to their database.