A pipe dream of mine is an open source WoW 1.12 client implementation. I wonder if anyone has ever attempted that. Bonus point if it compiles to javascript :)
Recently the turtle wow (a private server) team announced that they are working on a completely new Unreal Engine 5 client which sounds quit exiting. https://turtle-wow.org/turtle-wow-2
I think Blizzard hasn't bothered going against the open source servers because even if there's just a 1% risk that a court would rule agains them, it would open the flood gates to much more professional teams to come in and do it because "it's legal".
They do go against server operators sometimes, though they don't seem very determined there, and some servers have resisted successfully (hosting in Russia and identity hiding I think). I think they mostly use "you're using copyrighted assets" as a line of attack, precisely to avoid the risk that losing that would put them at risk. But IANAL.
Also note that in both cases the projects need the assets from a real client and don't ship with them, expecting you to provide them.
AFAIK the graphical assets are all in the client. The status data is for the most part available through (web)api and even more is available through client side interfaces.
Character and bank inventory including battle pets, achievements including dates, character stats, transformation unlocks such as different druid forms. Basically everything that would be required to 100% restore all the characters in a persons account exactly as they were on the commercial servers. A Full Backup of everything in ones account in a format the server can import so to speak.
You could decompile the game client if you wanted to, but that's probably more trouble than it's worth in most cases. Most of the business logic is in the server anyway, the client is just to initiate actions and render the world state.
(And similarly servers did not have the code, just assets + wire format between client and server, and they reversed engineered things from there, pretty successfully.)
The other is here: https://github.com/wowserhq/wowser, runs in the browser with WebGL, as you can see, it hasn't seen meaningful progress in almost a decade, but it is already impressive.
EDIT: Found the first one, PseuWoW: https://github.com/shlainn/pseuwow
More leads here: https://community.trinitycore.org/topic/12710-we-need-to-cre...