Preact

Official docs outline

Getting Started
Setting up Preact with a build tool or no-build import maps, and how it differs in size and philosophy from React.
Components
Function and class components, props, children, and the component lifecycle methods.
Hooks
useState, useEffect, useReducer, useRef, useMemo, useCallback, custom hooks, and the preact/hooks package.
Forms
Controlled and uncontrolled inputs, form events, and handling form state.
References
createRef, useRef, callback refs and accessing DOM nodes.
Context
createContext, Provider/Consumer, and useContext for passing data through the tree.
Signals
Reactive state with signal, computed and effect, and binding signals directly to the DOM.
Differences to React
Where Preact diverges from React: DOM events, class attribute, and the preact/compat layer.
Switching to Preact (compat)
Aliasing react to preact/compat to migrate existing React apps and libraries.
TypeScript
Typing components, props, hooks and JSX configuration in Preact.
Server-Side Rendering
preact-render-to-string, hydration and streaming server output.
Debugging Preact Apps
Preact DevTools, preact/debug warnings and common error diagnosis.
Unit Testing with Enzyme or Testing Library
Testing components with Preact Testing Library.

Each section links to the official page. Titles and summaries by Extra Credit; the docs belong to their authors.