With the massive exodus of wotc players, there are plenty of other games on the market. I figure here we can discuss and possibly compile games with fan licenses, open game licenses and creative commons/open source content and maybe a small addendum for systems that are public domain and can be replicated without fear of litigation. Im not going to do a fancy script on this but maybe we can make it into a doc or something later. So far this is what i've found.

Open Source or Creative Commons:
Pretty much free to use

OpenQuest Was OGL and is going creative commons as of Jan 11, 2023https://openquestrpg.com/
ICRPG by Runehammer Creative commons, extremely reasonable. https://forums.runehammer.online/t/content-creation-regulations/204
Barbarians of Lemuria by Beyond Belief Games https://championsoflemuria.boardhost.com/viewtopic.php?id=352


OGL
Adventurer Conquerer King System from Autarch: I think they've expressed intent to create their own open content policy, cant find anything official yet.
Basic Roleplaying from Chaosium Has an OGL, requires creators to use the most recent version of the license for any new work, but the license can continue to use the version it was published under for future print runs. If you publish under "BRPSRD1.0" and they update to "BRPSRD1.1" you can continue to use 1.0 for future print runs unless you change more than 30% of it's content. In which case you must use 1.1. https://www.chaosium.com/content/FreePDFs/BRP/BRP%20SRD%201.0.2.pdf
Savage Worlds from Pinnacle Entertainment Extremely lenient , but not open. The highlight here is they will never attempt to take your intellectual property. You retain all rights to your creation. They have a fan license (for homebrew and free content, basically says dont charge for it and dont use our worlds). Savage Worlds Adventurers Guild (you can sell your stuff and they collect 10%) and ACES (closer to a partnership, need this to sell outside of OBS) https://peginc.com/licensing/
Siege Engine aka Castles and Crusades Has an OGL, currently revising it to be proofed against abuses or retractions in the event the company ever gets picked up by a new owner they cannot rescind the license. Strong anyone can make stuff for our game policy.  htttps://trolllord.com/3rd-party-publishing/
Open D6 This one is weird because it cites the WotC OGL but was released http://opend6project.org/open-gaming-license/
GORE by Goblinoid Games An open game license, still cites wotc 1.0a but that will likely disappear as there isnt anything D&D in this game. Highlights here is they can change or retract the license at will but any work published under the current license can continue to do so indefinitely.
Shadowdark by Arcane Library Very open, in the works of creating a more fleshed out OGL but this is pretty much carte blanch to write stuff for their rpg https://www.thearcanelibrary.com/pages/shadowdark
EZD6 by DM Scotty Working with Runehammer, tailoring a custom OGL atm. If ICRPG is any indication it'll be pretty open. Creator answered in the discussion about an open license. https://www.drivethrurpg.com/product/397599/EZD6-Core-Rulebook

License Only
Requires a license but is not open content, you must have approval to sell
Mythras from the Design Mechanism Has a Gateway License, you only really need if you plan on making a product. Homebrew is fair game.https://thedesignmechanism.com/resources/Mythras%20Gateway%20License%20Public.pdf
2d20 by Modiphious Launching 2d20 worlds thats going to have a commercial content license. Details unknown currently. https://www.modiphius.net/en-us/pages/2d20
Dragon Warriors by Serpent King Games Only has a fan content policy, no official license. You cant sell anything made for dragon warrior, https://serpentking.com/2014/02/17/serpent-king-games-fan-policy/
Rolemaster and HARP by ICE Seems open to community content, cant sell supplements without a unique contract http://ironcrown.com/about-us/work-with-us/

Restricted:
Extremely restrictive or will not license
GURPS by Steve Jackson Games Will not license any aspect of this game. Notoriously difficult to work with on licensing 3rd party. http://www.sjgames.com/general/online_policy.html
R. Talsorian aka Cyberpunk Generally doesnt issue licenses, has a restrictive fan content policy but doesnt seem to go out of their way to issue take down notices. https://rtalsoriangames.com/homebrew-content-policy/

Monte Cook Games claims to have an open license, but it is a complete farce.

https://www.therpgsite.com/pen-paper-roleplaying-games-rpgs-discussion/monte-crooks-not-so-open-license-for-cypher-system/

I would like to say, that the Chaosium Basic Role Playing had a similar brew-ha-ha a few years ago.

They licensed the rights to RuneQuest to Mongoose who released it using the OGL. Then the license lapsed. Then time past. Then after about a decade since the original license was released they declared Mongoose didn't have the right to release it under the OGL and declared everything using that OGL illegal. They had the right, but after a decade it seemed monstrous. For some reason they allowed d100 games (OpenQuest) to have their blessing which made it seem a bit more random.

This thread is getting much more directly at what I had in mind with this one (https://www.therpgsite.com/pen-paper-roleplaying-games-rpgs-discussion/osr-games-that-are-or-will-be-free-of-the-ogl/) a few days ago.

The big item from that one is Shadowdark (from The Arcane Library). This is still in the future, but they've stated their intent to have their own OGL to allow people to publish material for their game. I believe Runehammer has a similar policy in regards to Index Card RPG, but I couldn't cite you a source.