While there are additional Layer 2 bitcoin blockchain technologies, this "Layer 2 Roundup" focuses solely on Lightning network ⚡ and Liquid Network 🌊.

Here's from a Tweet that describes this. It is not fully comprehensive, but places most of those I've heard of.

L1:
Most sercured monetary network ever existed.
Segwit, Taproot

L2:
Payment Network: Lightning
Tokens & NFTs: Liquid
Smart Contracts: RSK, Stacks, Sovryn