To the best of my knowledge, I’ve heard about a few other forums apart from Bitcointalk but the one that comes closest in structure and style is Altcointalk. The only downside is that the level of engagement there isn't as much as what we have here on Bitcointalk.

So if what you’re really looking for is something similar in format and experience, then Altcointalk is probably the closest you can ever get. I'll be reading the posts under this thread to see if there are relevant forums in the crypto space that I'm probably ignorant of.