In the contemporary Common Lisp ecosystem, software is distributed via Quicklisp[1], which is a centralized software repository, where, once a month, a new software distribution is created, encompassing the most recent releases of all software included in the dist. This means that changes in software can take up to a month to be reflected in Quicklisp.
Ultralisp is a Quicklisp-compatible distribution, except it's a bleeding-edge one. Each time a piece of software included in it releases a new version/release/commit, a new dist is created, and the modified software is available in Ultralisp within minutes.