In 2000, Wizards of the Coast pioneered this by releasing a SRD for Dungeons & Dragons 3rd edition under their Open Game License (OGL).
[1] The first SRD was published in 2000 by Wizards of the Coast (WotC) and is based on the third edition of Dungeons & Dragons; it was released under their Open Game License (OGL).
Instead of the full texts of the OGL-licensed rules, the 4e SRD presents only lists of concepts and tables from the 4e rulebooks that may be used in a compatible product.
Chase Carter, for Polygon in 2022, highlighted that the indie game design scene "has moved toward extremely permissible SRDs and the open plains of collaboration.
[...] SRDs, or whatever their next form might look like, may provide fledgling artists waystones through an open field instead of fence posts around private property".