Vue.js is a popular JavaScript framework used for building user interfaces and single-page applications (SPAs). It’s known for its simplicity, flexibility, and ease of integration with other projects. Vue.js allows developers to create interactive web applications by providing a reactive data-binding system and a component-based architecture.

Key features of Vue.js include:

1. Declarative Rendering: Vue.js uses a template syntax that allows you to declare the structure of your UI in a straightforward and intuitive way.
2. Component System: Vue.js encourages the use of components, which are reusable and self-contained units of UI. This promotes modularity and makes it easier to manage complex applications.
3. Reactivity: Vue.js provides a reactive data-binding system, which means that changes to the underlying data are automatically reflected in the UI, and vice versa.
4. Directives: Vue.js comes with built-in directives that allow you to bind data to the DOM, manipulate the DOM, and handle events. For example, the v-bind directive is used to bind data to an HTML attribute, and the v-on directive is used to listen to events.
5. Routing: Vue Router is a separate library that can be integrated with Vue.js to provide client-side routing for SPAs, enabling navigation between different views without full page reloads.
6. Vuex: Vuex is a state management library for Vue.js applications. It helps manage and synchronize state across different components, making it easier to handle complex data flows.
7. Lifecycle Hooks: Vue.js provides various lifecycle hooks that allow you to execute code at specific points in a component’s lifecycle, such as when it is created, mounted, updated, or destroyed.
8. CLI: Vue CLI (Command Line Interface) is a tool that makes it easier to scaffold, develop, and deploy Vue.js applications by providing a set of commands and a project structure.

Overall, Vue.js is a versatile framework suitable for both small projects and large-scale applications. Its gradual adoption approach allows you to integrate it into existing projects without a complete rewrite. The Vue.js community is active and supportive, offering a wealth of resources, tutorials, and plugins to enhance your development experience.