Offer the opportunity to refine and enhance your search. Many offer links to useful related material. Many offer a directory listing of popular sites. Minimal sorting of material returned, particularly of similar material at the same address. Different engines cover different pages, so you need to search in more than one.
All engines have slightly different rules for refining a search.
The results are then compiled into the metasearch engine. Some are able to eliminate duplicate records, or pages on similar topics at the same address. Some will sort your pages into topics, or will eliminate duplicate pages. Some don't sort the records very well, or will only show some of the search results to save space. When you search in a gateway you are usually only searching in the pages organised by people, although some will switch to a search engine if they can't find anything in their own database.