Kio's ZASM
Command line z80 assembler for Linux, BSD, OS X and,
hopefully, any Unix-like OS.
Supports the plain vanilla z80 stuff plus some ZX Spectrum
specific file formats.
Supports binary output and intel hex file.
Embedded Pascal Compiler Package (Shareware)
This first release provides compiler, assembler, linker and
simulator for Z80 and Z180.
Targeted for stand-alone applications (i.e. no operating system),
it allows you to use Borland's Delphi to design your
embedded application under Windows 95, or you can use it on its own.
Z80Sim
A Zilog Z80 simulator, debugger and profiler tailored for ZX
Spectrum development (but generic enough to be used with other
platforms), OS portable.