repl is a shortcut for read print eval loop. Usually this means "run an interpreter in an interactive way". REPLs exist for many languages: irb (ruby) php -a (php) scala
and many more.
vim-addon-async implements REPL completion for python and ruby (eventually scala).
Conque Shell allows running any terminal apps (including shells), but you can't use vim editing keys
There may be more implementations
Also see asynchronous-communication