Relay
Facebook's GraphQL client for React. 2015. Pragmatic + opinionated: fragment colocation, cursor-based pagination (Relay spec), static query analysis, Relay Compiler step.
Pitch vs Apollo Client: more strict, more efficient, but steeper learning curve. Other GraphQL clients (urql, Apollo) are easier to start with. Facebook + Meta use Relay for Instagram, WhatsApp Web, Threads, Workplace. Relay v17 (2024) introduced React 19 support + simplified config. Relay's pagination spec (connections, edges, pageInfo) is the de-facto standard in the GraphQL world even for non-Relay clients.