1)dart:io
File, socket, HTTP, and other I/O support for server applications. This library does not work in browser-based applications. This library is imported by default.
2)dart:core
Built-in types, collections, and other core functionality for every Dart program. This library is automatically imported.
3)dart: math
Mathematical constants and functions, plus a random number generator.
4)dart: convert
Encoders and decoders for converting between different data representations, including JSON and UTF-8.
5)dart: typed_data
Lists that efficiently handle fixed sized data (for example, unsigned 8 byte integers).