Steel Bank Common Lisp (SBCL) is a high performance Common Lisp
compiler. It is open source / free software, with a permissive license. In
addition to the compiler and runtime system for ANSI Common Lisp, it provides
an interactive environment including a debugger, a statistical profiler, a
code coverage tool, and many other extensions.
SBCL runs on a number of POSIX platforms, and experimentally on Windows. See the download page for supported platforms, and getting started guide for additional help.
The most recent version is SBCL 1.1.7, released April 29, 2013 (release notes).
In addition to the official SBCL, a Windows fork exists that adds support for threads on that platform as well. Though is has not
yet been incorporated into mainline, Windows users may want to consider
using it in the meanwhile.
SBCL's manual is available on the web in html and pdf formats. See the
doc/manual directory in the source code for the current version in TeXInfo source.
Bugs can either be reported directly to SBCL's bug database on Launchpad, or by sending email to the sbcl-bugs mailing list -- no subscription required.