CLSQL: database interface (I'm using PostgreSQL)
Weblocks: widget-oriented app framework with AJAX
Hunchentoot: web server
CL+SSL: SSL foreign interface layer
Babel: charset conversion
PURI: Portable URI library
CL-JSON
CL-WHO: HTML generation
CL-PPCRE: regular expressions
CL-OAUTH: OAuth implementation
Drakma: HTTP client
CL-SMTP: programmatically send email
Monkeylib-bcrypt: bcrypt foreign function interface
RESTAS is MVC, in the loosest sense of the word. The author, archimag, went way out of his way to make the "C" part, the controller, as flexible as possible.
RESTAS created its own module system on top of the Lisp package system. Importing a Lisp package from within an application also mounts that package's controller URLs underneath your app's.
He wrote one of the most authentic clones for Closure Template language. In fact, it generates HTML and JavaScript.
I could go on and on, but to put in a nutshell: the author actually looks at other web frameworks for inspiration, and is not someone trying to bolt an idealized "Lisp way" on top of the web. No continuations, no pretending that the web is a GUI, none of that crap. You want web, you get web: clean, modular, RESTful web.
[Disclosure: I'm the author of the ClojureJS library]