I am focusing on the 68000 because it is well, what I have, and Unix-like because, it is well, what I like

Downloads and details are here: http://subsole.org/mkmd
Nb: if you have a TT or Falcon, EasyMint or NetBSD are a much better start !
Edited:
MKMD has been replaced by ST Mint, based on Freemint 1.15 which will allow much more interesting stuff to work ( ethernet card !)
Get the new sd card image at http://subsole.org/st_mint.