  The Non-Fungible Token (NFT) market is mushrooming in recent years. The
concept of NFT originally comes from a token standard of Ethereum, aiming to
distinguish each token with distinguishable signs. This type of token can be
bound with virtual/digital properties as their unique identifications. With
NFTs, all marked properties can be freely traded with customized values
according to their ages, rarity, liquidity, etc. It has greatly stimulated the
prosperity of the decentralized application (DApp) market. At the time of
writing (May 2021), the total money used on completed NFT sales has reached
$34,530,649.86$ USD. The thousandfold return on its increasing market draws
huge attention worldwide. However, the development of the NFT ecosystem is
still in its early stage, and the technologies of NFTs are pre-mature.
Newcomers may get lost in their frenetic evolution due to the lack of
systematic summaries. In this technical report, we explore the NFT ecosystems
in several aspects. We start with an overview of state-of-the-art NFT
solutions, then provide their technical components, protocols, standards, and
desired proprieties. Afterward, we give a security evolution, with discussions
on the perspectives of their design models, opportunities, and challenges. To
the best of our knowledge, this is the first systematic study on the current
NFT ecosystems.
