Extensions make NFTs feature rich. What an extension can do is only limited by developers' imagination. Below are some possible extensions:
Compound NFT - extension that allows the NFT owner to interface with the Compound protocol.
Swap NFT - extension that allows token swaps.
Lottery NFT - extension that allows participation in loss less lotteries.
Loan NFT - extension that allows owners to take out an interest free/self repaying/regular loan.
DEX NFT - extension that allows others to exchange assets with the NFT. Think of this as a mini Uniswap. The NFT owner keeps all the fees from trades.
Breed and Battle NFT - extension similar to Axie Infinity.
Twitter celeb NFT - extension that allows Twitter celebs to make use of their Twitter clout.
Battle royale NFT - extension that has game elements from the likes of Fortnite.
Governance NFT - extension that allows owners to vote on governance proposals. Cam be specific to a protocol or generic.
Social media NFT - can you re-imagine your instagram account as an NFT? Each post is a mini NFT that is contained by the account NFT
Possibilities are endless.