Before any other layers came, we already have Bitcoin Lightening network, it's a base layer for Bitcoin and has existed for long time but the adoption is low and not use compare to the onchain transactions because using any layer other than Bitcoin original layer breaks Bitcoin privacy and your privacy and everything you do isn't too private like the typical Bitcoin network but the network is fast compared to the main Bitcoin network.

There is also one called Rootstock side chain to Bitcoin, this one has some special of Ethereum EVM, like you can run transactions on it layer and do all the transactions you like and be able to use smart contracts in transactions and you can convert your original Bitcoin from their own native network Bitcoin but all this still doesn't give you the privacy Bitcoin will gives you and this why Bitcoin network remain the best but transaction fee is discouraging a times.