A top-level command implementation vaguely reminiscent of Allegro CL's is available for CMUCL at Paul Foley's page.

E.g., it lets you type things like :ld foo to load a file, :exit to quit Lisp, and so on.

Peder Klingenberg has written a similar thing, at and there's an ACL-compatible REPL for SBCL included in the contrib directory.