Hasbro/Wizards of the Coast has released the core rulesystem of #5e #DnD under the Creative Commons By-Attribute 4.0 license. https://www.dndbeyond.com/posts/1439-ogl-1-0a-creative-commons
This is ONLY the System Reference Document (SRD), NOT the Player's Handbook or other supplements, and does not affect future versions of D&D.
This is a good thing. It's not perfect, because there is still a snake in the grass to be addressed (the Wizards Fan Content Policy https://company.wizards.com/en/legal/fancontentpolicy ) but my reading is that it's unenforceable.

