A non-fungible token (NFT) is a unique and non-interchangeable unit of data stored on a digital ledger (blockchain). NFTs can be used to represent easily-reproducible items such as photos, videos, audio, and other types of digital files as unique items (analogous to a certificate of authenticity), and use blockchain technology to establish a verified and public proof of ownership. The lack of interchangeability (fungibility) distinguishes NFTs from blockchain cryptocurrencies, such as Bitcoin. - Wikipedia

They are basically digital collectibles that anyone can download, but only people that own the NFT can sell.

Collect Greg DuBois NFTs with ETH

With your Ethereum (ETH) wallet you can collect Greg DuBois NFTs at the following link:
https://foundation.app/@GregDuBois

Collect Greg DuBois NFTs with XTZ

With your Tezos (XTZ) wallet you can collect Greg DuBois NFTs at the following link:
https://teia.art/gregdubois