Recently, @VitalikButerin said that Cross-L2 interoperability is no longer a problem. Although he did not specify the specific project, combined with the wonderful discussion in the comment area, I summarized some solutions that can solve the interoperability of Cross-layer2, as follows:

1）Based-Rollup

In the Ethereum layer2 camp, there are some projects that pursue compatibility equivalence. By allowing layer2 and layer1 to share components as much as possible, they achieve maximum compatibility with EVM, allowing layer2 to directly hand over the sorter function to the main network.

Specifically, when retrieving Mempool transactions, the Proposer of the main network can use a special route similar to MEV-Boost to capture the Rollup Batch transactions, and then directly complete the sorting and chaining on the main network. Representative project @taikoxyz

2）CrossChain-Rollup

The powerful ZK technology provides a possibility to establish a trust-free mechanism for homogeneous/heterogeneous chains in complex environments, including interoperability between homogeneous chains such as EVM-Compatible. Cross-L2 belongs to this category. In addition, ZK technology can also connect the interoperability of complex non-smart contract-based chains such as EVM and Non-EVM.

Specifically, the ZK technology framework will become an underlying communication protocol, which allows homogeneous and heterogeneous chains to complete absolutely secure and reliable message transmission by verifying proofs without checking each other's specific data. ZK-Rollup is essentially the process in which the off-chain layer2 calculates a large amount of data into proofs, and then allows the mainnet Rollup contract to directly verify and finalize. Representative project: @ProjectZKM's Enangled Rollup Network unified liquidity layer.

3）Intent-Rollup

Intent transactions have always been regarded as the key to the Crypto market's embrace of Mass Adoption. They can accommodate many related directions such as account abstraction, chain abstraction, AI Agent, Pre-Confirmation, etc. Intent transactions essentially "abstract" user needs to achieve programmable features, and then use a decentralized solver platform to execute user needs on behalf of others, thereby optimizing the user-side transaction experience.

Intent will be the final destination of the ideal transaction, which can lower the threshold for users to onboard into the Crypto market and attract incremental users to the industry. The intent track is not difficult to understand, but it is a huge challenge to program the user's vague and complex needs and then have the agent program execute them perfectly, which requires a huge solver processing network. Representative project: @dappOS_com

4）Layer2 Based-layer3

As we all know, the leading layer2 projects such as Arbitrum, Starknet, Optimism, etc. have successively launched layer3 application chain strategies. The layer3 application chain has customizable features, has its own independent Tokenomics, and can customize Gas, but it must rely on the basic components of layer2 to provide services, the most typical of which is interoperability.

The layer2 chain can provide a cross-application chain communication foundation for the layer3 application chain based on its own shared sequencer, shared prover, etc. Representative project: @arbitrum Orbit

5）Cosmos IBC Based -Rollup

Cosmos' IBC communication framework provides a basic interoperability capability for all chains connected to the Cosmos Hub. If the capabilities of Cosmos IBC are focused on the Ethereum layer2 ecosystem, a layer2 interoperability layer based on Cosmos IBC interoperability will be realized.

This solution will directly retain the core code of Cosmos SDK, while reducing development costs, while also enabling targeted additional development for the Ethereum ecosystem, allowing Cosmos' universal interoperability to be perfectly implemented in the Ethereum ecosystem. Representative project: @Polymer_Labs

6）AVS Based -Rollup

Eigenlayer's middleware service protocol implements a capability that allows Ethereum mainnet Validators to commercialize their own consensus and deliver it to other Rollup layer2 or other homogeneous/heterogeneous chains.

This solution essentially allows Ethereum validators to repeatedly stake LST tokens, and based on a set of reward and punishment economic mechanisms to constrain validators to expand outside the chain to construct a secure consensus on other chains. If layer2 uses AVS to construct consensus, it is equivalent to another economically driven Based-Rollup, and the mainnet components can participate in the cross-chain interactive process of layer2. Representative project: @alt_layer

7）Modular-Rollups

When modularization reaches a certain level, the Rollup as a Service paradigm will drive the prosperity of the layer2 one-click chain launch market. At that time, a layer2 network may share Celestia's DA data availability layer, Solana's VM or Ethereum EVM and other shared execution layers, as well as Ethereum as the shared settlement layer of these Rollups. In order to achieve absolute modular collaboration, cross-chain collaborative communication between different modules or different chains is a basic prerequisite. Representative project: @AvailProject

……other

Note: These are just a few of the directions I am familiar with, and they may not be complete. There are many projects working on the same direction and with differences, and you can add them in the comments section. (All of them aim to eliminate centralized cross-chain bridges and CEX asset transfer stations)