It is a modern reactive framework written in Dart. It provides Material, Cupertino, Widgets, Animation, Gesture etc.
It is written in C++ language and provides core library for graphics (through Skia), text layout, file and network I/O, accessibility support, plugin architecture, and a Dart runtime and compile toolchain.
It is a platform specific embedder which provides entry point. It communicates with the OS to access different services like Native plugin, App packaging, Thread setup etc. It is written in platform specific language exa. Java and C++ for Android, Objective C/ Objective C++ for iOS.