The old MS Word Sucks page captured a distinctly pre-social-media style of software rage: long, technical, profane, specific, and written by someone who had clearly fought the application for years.
Apollo programmer Don Eyles's long technical paper explains the Lunar Module guidance computer from the inside, including the 1201/1202 alarms, software restarts, throttle instability, and the tiny memory budget that still landed astronauts on the Moon.
A 1997 programmer joke turned Grady Booch's object-oriented modeling language into a church, complete with inheritance, superclasses, and a Booch Bible.
ToastyTech's Doom pages preserve decades of custom levels, alpha screenshots, joke skins, unfinished experiments, and the stubborn afterlife of a 1993 game.
DPGraph is a surviving late-1990s mathematical visualization program written entirely in assembly language, capable of interactive graphs extending well beyond ordinary three-dimensional plotting.
InterGuru has been converting address books between long-obsolete mail programs since 1996, preserving a wonderfully specific utility from the era when moving contacts between programs was its own technical problem.
Bjarne Stroustrup's personal site preserves decades of first-person C++ history, FAQs, design rationale, papers, standards work and the sort of direct technical writing that usually disappears into corporate documentation.
Futureware 2001 preserves an Austrian software collective's late-1990s and early-2000s projects, including translation tools, Linux software, SourceForge migration and distributed rendering experiments.