Nucleus is a draft proposal for Lightning multipeer payment channels which provides better capital efficiency (no inbound liquidity is required) and liveness. It also doesn't rely on a penalty mechanism and doesn't require the use of atomic swaps and routed payments for scaling.
"Lightning payment channels are the only solution for blockchain scalability problem available for existing UTXO-based P2P networks which doesn’t require consensus-breaking changes."
"Still, existing forms of payment channels are capital-inefficient and put high availability requirements on the participants, which reduces system utility and adoption."
"The current work proposes a new form of Lightning channels (named "Nucleus"), which can be created and run by multiple participants making their liquidity fully available inside a multipeer channel."
"This significantly increases capital efficiency, improves liveness and doesn’t require the creation or participation in an atomic swap routing network (Lightning network)."
"The solution can operate on top of any UTXO-based blockchain equipped with N-of-M threshold signature scheme(s) and timelocks, without introducing new consensus-level requirements of script operational codes."