Google›Google› offers Flutter

Flutter is an open-source framework for building natively compiled, multi-platform applications from a single codebase. Flutter code compiles to ARM or Intel machine code as well as JavaScript, and applications deploy to mobile, web, desktop, and embedded devices. The framework is supported and used by Google and maintained by a community of developers around the world.

Flutter is powered by Dart, a programming language optimized for fast applications on any platform, and its package ecosystem is distributed through pub.dev. The project site's content is licensed under Creative Commons Attribution 4.0, and its code samples are licensed under a 3-Clause BSD License.