Work in Progress
XCL is a new native-code implementation of Common Lisp. It features a kernel written in a restricted subset of C++ and an optimizing compiler, written in Lisp, with backends for x86 and x86-64.
XCL runs on Linux and 32-bit Windows.
The latest development snapshot is xcl-0.0.0.264.tar.gz (Jul 3 2009 09:29 AM).
On Linux, you should be able to build XCL by simply running make in the top-level source directory. If all goes well, you'll end up with an executable called x in the x subdirectory. Run this executable and do (sys::c-s-2) at the REPL prompt to compile the .lisp source files, then restart.
Building on Windows should be equally straightforward if you have the right toolchain setup, which is basically MinGW and MSYS (I'm currently using g++ 3.4.2 and make 3.79.1).
The latest snapshot fails 269 out of 21581 tests in the XCL fork of pfdietz's ANSI tests, included in the tarball (use RUN-ANSI-TESTS to run the tests). But on a brighter note, it successfully builds the latest CVS version of SBCL (1.0.29.54.rc2) on Linux x86[-64], and it passes the test suites of CL-PPCRE 1.3.0 and Ironclad 0.22.
License is currently GPL (I plan to add something like the Classpath exception when there's an official release).