Short answers, pulled from the story.
The Open Game License arrived in 2000. This legal framework allowed publishers to copy core d20 system elements without fear of copyright lawsuits while strictly forbidding the use of trademarks such as Dungeons & Dragons or D&D.
Matthew Finch edited the Player's Handbook for Castles & Crusades before launching his own project called OSRIC. Stuart Marshall later took over and published this release in 2006 which served as a catalyst for other designers to create similar systems.
Daniel Proctor responded by writing Labyrinth Lord which appeared in 2007. He based his work on the 1981 Basic Set edited by Tom Moldvay and the Expert Set written by David Zeb Cook.
Swords & Wizardry offers three distinct versions: White Box, Core, and Complete. The White Box omits later expansions to mimic the pure 1974 experience.
Chris Gonnerman released Basic Fantasy RPG in February 2017. He updated the game through June 2023 while separating race and class and using d20-style ascending armor class.
Mazes & Perils expands play from level 3 up to level 12 and won an ENnie Award in 2013. This expansion of levels distinguishes it from other retro-clones that may have different progression limits.