If you build web apps, and need users to be able to connect to their wallets and sign transactions through your apps, you'll want Solana's Wallet Adapter.
For real-life examples of using the Wallet Adapter in your React based web and mobile applications, check out this directory.
Unified Wallet Kit
Unified Wallet Kit is an open source easy-to-integrate Wallet Adapter, that is built on top of Solana's Wallet Adapter. Here are code examples:
TipLink is an easy-to-use, non-custodial wallet that makes transferring funds as simple as sharing a link. Think of it as pre-paid gift cards, except that the gift cards are actual wallets that the user has full control over.
Many other wallet managers like dynamic.xyz, Magic Link, and Web3Auth offer social-embedded (Email, Google, Apple etc.) wallet creation as well as via SSO.