Oh, I think I may found out how you save people's progress.. Probably is that ignoxx(aka OP) .gmk socket engine. It's on github. You can confirm me if this is the case.
I've recently renewed my knowledge about swf lately. There are like 2 ways communicating with the server from within the swf. Either through xmlnode? php/flashvars, or creating a socket. (aka emulator) for anyone who is interested. Probably this is how private servers once worked. NOw idk. about executables, but probably they're using the same mechanism. Always wondered why you didn't make an online version of gmk remixes, probably because they're slow. And crash repeatedly.
Imo, if you really want to create a game similar to 2006-2008 DO/SF you should follow their steps made back then. i still think you can use a .swf for online, instead of a game maker or unity engine. 2005-2006 tech was pretty simple, yet they did wonders with that. Just think about IT. They didn't need tertiary programming languages or anything ugly and hardware-consuming like that, not even failed game engines. But it was exploitable, perhaps going back in time to 2006 Do it would have been easier to crack than now. They stuffed their shitty game's egine with useless pieces of code. YOu can still see the swf if you know how to crack their main .exe client. But time is needed.
Somebody should ask DO devs, how much time they took for that project. I mean original devs. Everyone from nowadays bigpoint isnt the same with original BP team from 2004-2011. probably is this. All original devs left. You're now left with the replacements hired from 2012-13, including in the art department. bp is nothing more than a company which was thrown around here and there with the owner being the highest bidder(see youzou company), I still think this is the opera of the original CEO anyhow, sold everything and had idiotic ideas, which made the game as it is today. Whole game dev industry is like this.
Profiting this much they should also probably make an avatar mmo pitch, just like they did in 2012 with that BSGO lol. I am sure they will love their money. Since this franchise will be up to 2028. then shutting it down disappointing all of the old fanbase(because they don't care about you).. There should be a rule when shutting down a game, they should also release the source files. since they won't be needing them anymore. Letting everyone start their own sandbox singleplayer server. or at least put the resources/images in some sort of repository. BUt inb4 i forgot, they use the same source code for all of their games lmao, but only re-skinned, see seaifght-DO game mechanics look alike. What is changed only the sprites.