Ionic is a html/javascript/css mobile ui framework using web components, with bindings for Angular, React and Vue. You can build PWAs, mobile web apps, or with Capacitor actual mobile apps with it.

Capacitor is a mobile app toolkit for building apps with web technologies in a webview. Effectively the successor to Cordova/PhoneGap. It’s built and maintained by the same team/company as that behind the Ionic framework.