This is the System Reference Document (SRD) for METTLE Core. This game uses a CC-by 4.0 license to encourage others to use this system in their own creations. CC-by means reusers may distribute, remix, adapt, and build upon this material in any medium or format, so long as attribution is given to the creator. This license allows for commercial use.
To use for your games, just cite this or similar:
“This work is based on the text of METTLE Core; a product of Planarian Games, developed, authored, and edited by Jake Eldritch, and licensed for our use under the Creative Commons Attribution 4.0 International License: http://creativecommons.org/licenses/by/4.0/