ARK is a new type of Layer 2 protocol with the UX of E-Cash but non-custodial. When it was announced first in 2023 it was clear that it would require a soft fork like CTV to even work though. Now 2 years later it's here live on Bitcoin mainnet, without the need for a new soft fork at all.

And with the interoperability with Lightning it will create some interesting wallets and new use cases.