Considered switching from my own to MyBB/phpBB. I can't recall exactly which two they were, but I believe those, as they were the only free options that I could one-click install. However, after playing around with them for far too long, I reconsidered my position on an external communications platform as I wanted engagement to remain on my text-based RPG, so members wouldn't lose focus on playing too much.
I have used a wordpress (used multiple forum plugins), SMF, MyBB, phpBB and XF. I started with Wordpress because it was really easy but had to move to SMF because wordpress forums had limitations. Of all open source I have used, I think SMF is good. I am using XF because most people are using it.
Throughout the years I've used MyBB, phpBB3, SMF, Woltlab, Invision, Xenforo, Zetaboards, InvisionFree, Jcink, BraveNet, FluxBB, PunBB, XMB and I tried Flarum a little bit. I'm currently using ForumSpark on a test board and I'm really liking this free hosting, it's like Zetaboards like mentioned in the thread. Of course this wasn't on the same forum, these were all different forums I've had throughout the years and honestly a lot of them were for testing purposes because I wanted to try out different forum software. I'm currently using SMF, Woltlab and soon vBulletin for another forum once it gets migrated over. I switched from Xenforo to Woltlab because I didn't like the direction the staff were taking with the software at the time. They were taking too long for updates. The forum that will be hosted on vBulletin's cloud servers I felt needed more than what phpBB offers so that's why I switched plus they had a sale going on at the time.