SLIME
The Superior Lisp Interaction Mode for Emacs
...While lisp-mode supports editing Lisp source files, slime-mode adds support for interacting with a running Common Lisp process for compilation, debugging, documentation lookup, and so on. The Read-Eval-Print Loop ("top-level") is written in Emacs Lisp for tighter integration with Emacs. The REPL also has builtin "shortcut" commands similar to those of the McCLIM listener. SLIME is able to take compiler messages and annotate them directly into source buffers.