RetDec is a retargetable machine-code decompiler based on LLVM
...Static analysis of executable files with detailed information. We currently support Windows (7 or later), Linux, macOS, and (experimentally) FreeBSD. An installed version of RetDec requires approximately 5 to 6 GB of free disk space.
ATasm is a 6502 command-line cross-assembler that is compatible with the original Mac/65 macro assembler released by OSS software. The aim of ATasm is to provide Atari home-brew coders with a comfortable and powerful toolset.
pyz80 is a z80 cross-assembler written entirely in Python. It accepts text files with the syntax of the Sam Coupe's popular COMET assembler, and outputs a disk image suitable for loading in SimCoupe or transferring to floppy disk for use with a real Sam.