MimbleWimble protocol is a slim-down version of BTC protocol and aims to improve scalability and privacy.
scalability
MimbleWimble focuses on creating new protocols which make running nodes less resource intensive. other projects focuses on centralization and state channels solutions. MimbleWimble is a UTXO-based system, not a state-based system. MimbleWimble gets rid of old and unneeded transactions, which both have large ledgers on BTC and ETH. MimbleWimble's ledger is not burdened by historical data transactions. the ledger's size will always be megabytes.
privacy
MimbleWimble uses Confidential Transactions protocol. this protocol allows users to hide the input and output values, making the information available only to the sender and receiver. MimbleWimble uses CoinJoin protocol. this protocol combines various transactions into one big transaction, where all senders send money to all receivers. by combining Confidential Transactions and CoinJoin, MimbleWimble eliminates the need for traditional signatures per transactions, public keys, and addresses.
https://coindoo.com/what-is-mimblewimble-what-do-we-know-about-grin-and-beam/