Ask HN: What are the “Great Wonders of Software”, the greatest software built?

Unisys MCP & MS-DOS. Two Operating systems.

MCP on Unisys mainframes was the most reliable Operating System I ever used.

MS-DOS started the world domination of Personal Computers, after a few false / failed starts by other desktop Operating Systems.

Linux, LibreOffice, Firefox, KDE Plasma desktop

The firmware my coffee maker runs is #1