The Portable C Compiler (pcc) is a multi-target C compiler, supporting the C99 standard with additions from later revisions. It is small and simple in its design, and as of today around 16 targets are available that will generate code (to some extent).
The compiler is based on the original Portable C Compiler by S. C. Johnson, written in the late 70's, even though lot of the code has been altered to support more modern standard.