Regarding the example, Star Wars Galaxies, here's the info from the SWGEmu project itself (
http://www.swgemu.com/forums/content.php?r=173)
Q. Has SWGEmu ever seen Sony Online Entertainment's code?
A. Absolutely not. In fact, Sony Online Entertainment persists that they have lost the code entirely. Not only does this make it impossible for SWGEmu to utilize the code as reference if Sony Online Entertainment was kind enough to grant permission to do so, but it makes it impossible for Sony Online Entertainment to release classic Pre-CU servers to rival what SWGEmu aims to accomplish.
Q. How does SWGEmu develop the software without Sony Online Entertainment's code?
A. SWGEmu's software is written through a process known as Reverse Engineering. By applying the Scientific Method, SWGEmu's developers observe game-play, and then attempt to recreate it's experience through programming.
Q. What about the application I install from the discs I purchased from Sony Online Entertainment?
A. When you install and connect to a SWGEmu server with this application, you are doing so by your own accord. SWGEmu cannot condone the usage of the Sony Online Entertainment client application with it's server software, and users should be warned that they are in breach of the Sony Online Entertainment EULA when they do so.
Basically, the client side is the code you bought to have on your computer. Since you already have it, you can do with it whatever you privately want (to a certain extent, mind... no selling it, no decrypting it, etc, but you can run it all you want.) The server side is the problem, in that Sony hasn't released it, and that if there's a rogue server, Sony may indeed come after the server AND the person(s) running a client to connect to it.
Maybe. Be a freakin' nightmare if they did that past the server, as a big ol' bad comin' after a wee lil' bitty is just not cool, legally or not, in the Public's View(tm), especially for a closed game. "Why do you even care?!" they'd cry.
But further, there's NO server code. So all they're doing is a very difficult reverse engineering, seeing what the client wants and attempting to replicate the need as best they can figure out, as well as any enemy/friend location, action and what not being served back to the client. This in and of itself is just a tiring trial and error.
Sony *says* the code does not exist (for the code they're trying to replicate with the SWGEmu is one previous to the last couple of updates which 'broke' the game enough that people quit), so they're doing it completely from scratch, listening to clients, analyzing the data, making code to do this or that, and repeat.
Ugh.
But sure... you can play that, if you want. Heck, it may be 90% perfect, but that 10%...
And regarding legality, in case that matters:
Q. Is SWGEmu legal?
A. This question pops up about once per month on our forums, but the never changing answer is simply, yes. Understand, there is a fine line which SWGEmu has yet to cross. Since SWGEmu doesn't distribute any of Sony Online Entertainment's copyrighted material, it does not break any copyright laws. SWGEmu works very hard to stay within it's legal right to produce it's software, and will do it's best to never include copyrighted materials, or infringe on any software patents.
This is important. That the code is being done from scratch on the server side means that they just are pushing numbers around in code that's *completely* not Sony's. That it just happens to work with the SOE client for SWG is... well, not happenstance, but happy coincidence, let's call it.
It is as they say a fine line.
But there's one other thing mentioned somewhere in there. They started this *when Sony 'broke' it with that bad (to the players) update.* That means they had a head start on what was going to need to happen, *way* before the close of SWG. The Combat Upgrade happened in 2005, and then they started this project some time after that. That is now *10 years* of coding and experiments, potentially. Whereas in the CoH example, there was 3 months and poof, and now it's been only 3 yaers and change.
So you need to give CoHEmu more time, ok? Ok.
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This is but ONE example, the biggest, I'd think, of the SWG issue. Unless someone's got a rogue copy of the real deal, last update to it (which apparently is highly disliked compared to the Pre-CU anyway) then what you're seeing is a nearly decade old project still going on, and openly recruiting people to try it out. And if they DO have a real deal, Sony code server set up... you won't be seeing that on the Googles or anything, but a Dark Web sort of thing.
Good luck on that invite!