Meant to destroy the productivity of Lisp programmers worldwide, cl-twit is a Common Lisp client for Twitter, with an emphasis on using it from the REPL.
Browse the source online at github, or get it using:
git clone git://github.com/chaitanyagupta/cl-twit.git
You can also visit the downloads page.
There's a manual too.
cl-twit is maintained by Chaitanya Gupta. Send him feedback at mail at chaitanyagupta.com, or ping him on Twitter
Trivia: cl-twit came out within a week of two other twitter clients being released for CL. Both are named 'cl-twitter'. One is by Ian Eslick, and the other is by Chris Davies.