ForumEngine looks promising. It could be a perfect alternative for vBulletin.
It's phenomenal, outstanding, gorgeous and intrigues a user to stick on site. Surely, it contains lot of charisma in itself. Kudos to whole team :)
I’m familiar with EngineThemes’ excellent work. I often recommend ForumEngine to folks interested in adding a forum to their site, it’s gorgeous, and one of the best forum solutions I’ve seen.