XCL is a Common lisp implementation
licensed under GPL
It has been developed by Peter Graves, the author of ABCL.
Its main features are a small C++ kernel for bootstrapping, its own native code compiler, compact code, native threads on both linux and win32.
Its aim is to be as compliant and portable as possible, be easily embeddable as ECL, fast as SBCL, compact, clean, ...
Package structure resembles the one of ABCL. Also, seems like a lot of code is shared between these two implementations.
It is still in very early stage (version 0.0.0.274)
Source code can be found here
XCL is now on GitHub:
git clone git://github.com/gnooth/xcl.git