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

CLiki the common lisp wiki