The BYU Family History Library has a lot of resources that would interest genealogists. It's located in Utah, and is connected with the popular FamilySearch website. It also seems to be connected with the Harold B Lee Library. You can visit the physical libraries themselves if you want to. I would suggest checking the website before you go, because they appear to have an unusual system regarding when these libraries will be open. Otherwise, you can access information from the BYU Family History Library website instead.
Most of what you can access from the BYU Family History Library is in the form of a series of links. Some of these links will lead you to other, very specific, search engines. For example, if you start by clicking on the link that says Records you will see a long list of resources that connect to websites or libraries that have official documents in them. If you click on the link in that long list for Ellis Island Records Online, you will be redirected to the official website for Ellis Island. It has it's own search engine for you to use. On the other hand, if you click on the link for Census Online on the BYU Family History Library, it takes you to the official Census Online website, which you have to click through in order to navigate through the website and locate what you were hoping to find.
The section called Selected Internet Research Sites gives you a long list of other online resources. There is a sublist of United States sites, Canadian sites, and European sites. There are websites to help you with geography, and ones that are an archive of photos or videos. You can find a list of useful Wiki sites here, and more. The Reference category includes genealogy related blogs, indexes of periodicals, and even some world maps. There is a link to connect you to books that are owned by the BYU Family History Library, a resource that is completely unique to this website. I like that they have included links to dictionaries and encyclopedias, including a dictionary of genealogy and archaic terms. There is a lot here for genealogists to use.