Yes Bitcointalk, Altconstalks and another all forum build by SMF and it is early to install. anyone can get source code from github and use that code. Creating a forum is easy but gaining popularity for it is not easy. Bitcointalk was the first crypto forum to be created to discuss about Bitcoin and that's why this forum gained its popularity along with Bitcoin. Some user already posted SMF link and Github link here so again I didn't post
You have forgot to mention that Satoshi Nakamoto was also part of this forum and if someone tries to create a similar forum using Simple Machines Forums then that user should also think something about the Satoshi Nakamoto. That forum won't be close to this forum because various bugs have been patched on this forum and those bugs aren't patched on original SMF code and that's why if someone installs a fresh copy of SMF on their forum then that person should better know the drawbacks of that open source code.
I also believe that the original source of the forum isn't public and it will remain closed source because theymos doesn't want the hackers to find vulnerabilities in the code and then exploit those vulnerabilities to steal private data of the users. I'm quite sure that only theymos and a few close developer friends of him are aware about the source code of the forum and they are the only ones who may view the source code and fix bugs on that source code. But, sometimes I think that only theymos knows about the code of the forum and he may fix the bugs himself.
