SDCC is a free open source, retargettable, optimizing ANSI C
compiler suite that supports a growing list of processors including the
Intel 8051, Maxim 80DS390, Zilog Z80, Z180, Rabbit 2000, gbz80,
Motorola 68HC08, S08 and STMicroelectronics STM8 targets. There also is incomplete support for the Microchip PIC16 and PIC18.
Good and useful software
simple and easy