21. cclan
    The Comprehensive Common Lisp Archive Network.
22. cffi-posix Berkeley sockets
    cffi-socket - CFFI wrappers for Berkeley sockets
23. cffi-posix Linux extensions
    cffi-epoll - CFFI wrappers for Linux extension EPOLL
24. cffi-posix POSIX headers
    cffi-posix
25. CGI
    The Common Gateway Interface (CGI) is an interface for running web applications as independent executables under the control of a webserver
26. cirCLe
    cirCLe is dead, or at least has seen no active work since 2004 or so
27. cl-schedule
    cl-schedule: A scheduling library in CL
28. CLiki Sandbox
    Building from Scratch
29. CLOS
    The Common Lisp Object System is based on generic functions, multiple inheritance, and declarative method combination
30. Clozure
    Usually refers to Clozure CL

CLiki the common lisp wiki