Ionic is an open‑source UI toolkit that lets developers build native‑quality iOS, Android, and Progressive Web Apps from a single codebase using HTML, CSS, and JavaScript, with built‑in support for popular web frameworks like Angular, React, and Vue. It’s aimed at front‑end and mobile developers who want to create fast, responsive cross‑platform apps (including PWAs) without juggling separate native codebases. The framework is especially suited for teams looking to leverage Web Components and modern web standards while still delivering a truly native user experience.