There are several shells for Emacs, but none can match the versatility and integration with Emacs like Eshell. Eshell is a shell written entirely in Emacs-Lisp, and it replicates most of the features and commands from GNU CoreUtils and the Bourne-like shells. So by re-writing common commands like ls and cp in Emacs-Lisp, Eshell will function identically on any environment Emacs itself runs on.
You can have a complete overview on this youtube video: https://www.youtube.com/watch?
= Overview =