A System Refence Document (SRD) contains the rules, information and licensing details needed for TTRPG designers to create their own games using that system. I have tried to avoid adding projects that are an RPG system without the SRD element, but sometimes the distinction is not clear. I have tried to ensure that every SRD is provided by the system creator or with their permission, but if this is not the case with any of these, please let me know.
PLEASE NOTE: Some of these use the OGL 1.0, which at the time of writing might cause legal issues going forward. Please check the licensing information on every entry carefully.