Bitcoin transactions are pseudonymous, but publically traceable on blockchain. Many altcoins have stronger privacy primitives.

• MimbleWimble: Combines transactions, hides amounts and addresses and uses confidential transactions in order to obscure metadata.
• Stealth addresses (e.g. Monero), ring signatures, and mixing inputs.
• Zero Knowledge Proofs (e.g. Zcash): Allows users to completely shield transactions, proving their validity without disclosing details.