OpenSea claims on its website that it’s the biggest NFT marketplace. It offers a big selection of non-fungible tokens that include art, virtual worlds, trading cards, and collectibles. The site features more than 700 different projects and lets creators create their own items on the blockchain by means of the site’s item mining tool. If you’re selling items on OpenSea, you can sell it for a fixed price, create a declining price listing, or set up an auction listing.