How to make a NFT marketplace only for my own NFT program?

I am trying to create a marketplace like this: LetMeSpeak Marketplace Beta. As you can see, users can filter the NFT by rarity, price, etc. I am wondering, are they use metplex for this or write the Solana program by themselves to provide this functionality? Or it’s just a REST API in which data come from a SQL database.

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