Flutter is an open-source application development framework by Google and is capable to develop both Android and iOS apps.
Flutter – Open Source Mobile Application Development Framework
Flutter is not just confined for creating apps for android and iOS, but can also be used to develop web apps for desktops. It is a user interface toolkit, using it several apps can be designed from a single codebase. Google dedicated a lot of attention towards this app building framework from the beginning of 2019. It is a software development kit that helps build high-fidelity, high-performance apps. The main objective is to allow designers to deliver high-performance apps which look pretty natural in different mediums.