Quix hosts NFT collections deployed on the Optimism Layer 2 network, while Stratos hosts NFTs on the Arbitrum Layer 2 Network.
We're also working on adding support for bridging Layer 1 NFTs to Layer 2, which will likely be available in the coming month. This will allow owners of NFTs on Layer 1 to convert them to Layer 2 and sell/transfer them there at a fraction of the gas cost.