ASDF provides the functionality of make and ld.so for Common Lisp software: It drives compilation and dynamic loading for complex Lisp systems with multiple modules and files, and is the de facto standard used by free software written in Common Lisp.

It also includes a utility library, UIOP, to portably deal with many issues that all Common Lisp programs have to deal with, including handling pathnames, accessing the filesystem, executing external programs, user configuration, etc.

Most Common Lisp implementations already provide asdf via (require "asdf"), but not all of them provide an up-to-date version.