I was shown a link to an incredible 64 byte MS-DOS demo called into war by HellMood/DESiRE.
It doesn’t actually depend on MS-DOS however, using only BIOS calls and PC hardware, so it was easy to turn it into a boot sector. We can use nbdkit-data-plugin to run it from the command line:
nbdkit data data=" 49 192 80 185 255 0 190 0 1 191 254 255 189 28 9 20 19 186 48 3 243 110 205 16 184 79 12 230 64 226 247 31 104 0 165 7 184 205 204 247 231 137 232 128 238 246 246 246 146 44 127 246 234 2 22 108 4 146 48 198 246 238 212 9 156 157 44 116 170 175 235 220 201 56 153 70 103 81 127 @0x1fe 0x55 0xAA" --run 'qemu-system-i386 -hda $nbd'
you can try https://flatassembler.net if you like assembly programming …