Tripadvisor - A key search engine for local services, hospitality and entertainment. Among others, user reviews seem to be a crucial ranking factor for local searches in catalogues like these.
Booking - One of the many search engines in the realm of accommodation and travel. Not only are the hotels trying to rank on Google but also on Booking and other similar websites.
YellowPages - Formerly in paper form, now in digital, YellowPages is a search engine primarily focused on local services. Over time, their function has been partially replaced by Google.
Amazon - In many cases, Amazon is the ultimate website where the user journey, that once started with an inspirational or transactional query, ends. After users gain the necessary product information from YouTube reviews, blog posts or comparison articles, they end up at Amazon doing the final search and making a purchase.
Facebook - What once started as a platform for connecting friends, ended up as a search engine for individual people and their interests. Worth mentioning is also Facebook Marketplace as a global search engine for second hand products.