GNU Common Lisp

GNU Common Lisp (GCL, formerly known as Austin Kyoto Common Lisp) is a compiler and interpreter for Common Lisp. GCL is very portable and extremely efficient on a wide class of applications, and compares favorably in performance with commercial Lisps on several large theorem--prover and symbolic algebra systems. GCL supports the CLtL1 specification.

Some advantages

Go here to download the source (good for unix), and a linux compiled version.
The source is now under cvs and you can download various versions, including any changes.

William F. Schelter