This paper identifies the most important innovations in software, removing hardware advances and products that didn't embody significant new software innovations.  Its results may surprise you.

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A comprehensive historical survey of the most important software innovations from 1837 to the 1970s, carefully distinguishing between hardware advances, product releases, and genuine software innovations. The list covers foundational concepts like stored programs, subroutines, compilers, garbage collection, object-oriented programming, packet-switching, TCP/IP, relational databases, GUIs, and more. The author defines strict criteria: innovations must be widely used, technologically novel ideas (not mere re-implementations or hardware), and critically important. Notable exclusions include hardware milestones, popular products that were simply re-implementations, and social/legal inventions like open source licensing. The paper also examines the relationship between software patents and innovation incentives.

The Most Important Software Innovations

What’s Not an Important Software Innovation?

Appendix: Software Innovations Being Considered