GCL is a Compiler and interpreter for Common Lisp. GCL compiles to C and then uses the native optimizing C compiler (e.g., GCC), giving great portability. It is highly efficient: a function call is basically the same speed as a C function call, in fact identical to a C function call via a pointer.
The program has a source level Lisp debugger (dbl) for interpreted code, letting you step a line at a time, while displaying your position in an Emacs window. It has pioneered conservative Garbage Collection schemes, but also has the stratified garbage collection (SGC) scheme, for only recent allocations, that is based on native page fault handling.
There is also a built in interface to Tk widget system. Allows a mixture of tcl and common lisp to be used in a user interface--your choice which you use.