No, Adsense is not the only website that you can use to earn revenue on YouTube. Many Youtubers earn from affiliated marketing, they earn from websites like Amazon, they are paid for every click that leads a purchase of a product.
Others earn from paid sponsorships from brands like Microsoft, P & G just to name a few. Selling your own stuff is also another great way to generate revenue through YouTube.
You need to have an AdSense account if you want to earn through ads on your videos. Besides this you can also do affiliate marketing, where you pair with amazon or other e-commerce giants and promote a product. They will then give you a share of the revenue if anyone clicked your link and bought the product.
Moreover, YouTubers can also earn by doing paid promotions where businesses pay them to review certain products in their videos. The more views you have the more you will be approached by different businesses. Another hot thig is merchandise. Many YouTubers have their own customized merchandize for followers, which increase revenues.