What are some REPLs for Emacs Lisp?
Is there only one that is within Emacs?
Are there some that run inside terminal outside Emacs?
There is a (work in progress) REPL for Emacs for use from the command line. It currently supports basic command line editing and history.
The code is hosted on Github.
There is this project on Gitlab. The REPL can run on a termninal or on Emacs' minibuffer. Even if you run it in "no-window-system" mode (with -nw).