OpenLisp is a KISS (Keep It Simple, Stupid) full conforming implementation of ISO/IEC 13816:2007 ISLISP Language, the International Standard version of Lisp. Entirely written in C, OpenLisp has been ported on more than 90 different architectures (compiler/OS/processor) from small 16 bits MS-DOS systems to 64 bits systems such as DEC Alpha processor. All major processors (Intel 16/32 bits, Intel IA64, AMD/Intel EM64T, Sparc 32 bits and UltraSparc 64 bits, Motorola 68k and 88k, RS6000, PowerPC, MIPS R3000/R4x00/R8000/R10000, HP PA 32 and 64 bits mode, Alpha 32 and 64 bits mode, IBM s390, StrongARM, VAX) are supported. It even runs on Pocket PC.
OpenLisp is essentially a very fast interpreter (see benchmarks) that competes in speed with some CLtL compilers. It also has a compiler that produce LAP to be interpreted by a native virtual machine. You can even make standalone applications using the C code backend that also will make your code run from 10 to 20 times faster. OpenLisp is written in ISO C for the kernel and using POSIX like interface for the operating System when available.