The GraphQL Summit Worldwide 2021 conference covered various topics including client-side GraphQL, federation, subscriptions, and testing. Apollo released new tools to help developers build better with GraphQL, such as Apollo Studio's GraphQL IDE, Rover CLI tool, and Apollo Workbench. The conference also featured talks on client-side state management, testing React Apollo Client, mobile app development, architecture, and federated data graph usage. Key speakers included Ankita Kulkarni, Adhithi Ravichandran, Ellen Shapiro, Martin Bonnin, Mandi Wise, Faraz Ahmad, Kyle Schrade, Jason Lengstorf, Taz Singh, and Ash Narcisse. The conference aimed to provide insights into GraphQL best practices, tooling, and architecture for a wide range of developers.