The leading candidate is Web3Auth, which offers a suite of libraries for building simple, non-custodial authentication infrastructure. It spans multiple chains, including Ethereum, Bitcoin and Solana, and offers features like Multi-Factor Authentication, Fiat-to-Crypto API and a whitelabelable Wallet UI. Web3Auth is designed to be modular and blockchain agnostic, so it can be used in a variety of Web3 projects.
Another strong contender is Dynamic, which offers a full-stack platform for logins, wallet creation and user management. It supports multiple chains, passwordless login with Passkeys, and built-in on/off ramps for converting fiat money into cryptocurrency. Dynamic also offers TSS-MPC technology and multi-chain support, so it can be used in everything from NFT marketplaces to DeFi apps.
If you're looking for something more geared toward enterprise, check out Moralis, which offers a suite of Web3 APIs for quick access to cross-chain blockchain data. Its APIs offer features like real-time market data, node management and cross-chain NFT transfers, and are designed for building scalable crypto and blockchain apps. Moralis supports multiple EVM chains, meaning it can be used with a variety of blockchain networks.