These programs are the result of following Big Evil Corporation's amazing series on developing for the Mega Drive, with some assistance from René Richard's 68k tutorials repo.
I've been using asmx multi-CPU assembler due to its support for Unix and 68k assembly language. You'll need to compile it from source, but this is achievable with GCC. Note that you'll need to grab version 2.0 beta 5, as this is the only version to support end-to-end binary output, rather than merely providing object code.
To assemble the hello world example:
$ cd helloworld
$ asmx -e -b -C 68k main.asmThe produced binary (main.asm.bin) can be loaded by any emulator or even run on real hardware. I'm using BlastEm due to its 64-bit Linux support and debugging tools.