https://archive.org/details/Microsoft_Editor_Assembler-Plus_1979_Microsoft

Pretty sure I remember plunking down hard-earned lawn-mowing money for this software, back in the day. Before that, I had done all my machine-language programming by hand-assembling opcodes with pencil and paper. This was a huge step up for me (macros!), and I still have fond memories. (Of course… I never actually wrote a complete program with it. )