I've ran a number of forums since 2005, started off using Proboards, phpBB2, IPB (sold the license after 2 weeks) then vBulletin. I'm liking what I see with Flarum, the potential is vast if the focus remains on content delivery, scalability and intuitive UI it may loosen the grip of the bigger players.
I have to say I have struggled to find a software that I'm completely happy with -- content focused, light weight and doesn't require constant resuscitation from the backend to stop it collapsing in on itself. I'm not big bloated forum scripts like Xenforo, IPB and SMF. I dabbled in phpBB3 since Beta and find it archaic and imposible to scale without constant attention. At present I am using Discourse on a VPN, hosted vanilla and a too heavily modified version of vBulletin 4 to even consider migration.
Since social media grew to the scale it is at now, I find it difficult to recuperate the costs of maintaining a forum, so licensing and server costs are a major factor. Gone are the days of paying a couple hundred for a years licensing and hosting. Not including paying for themes and extensions or man power in tweeking things.
