Putting the forum up is one thing, the code is available:https://github.com/voat/, and there are others like Lemmy; https://github.com/LemmyNet/lemmy. Keeping it up, I imagine, is quite difficult and expensive. Forums are tough because of there dynamic nature, there isn't as much that can be done in terms of caching or preloading content. I think the whole model needs to be rethought.