This forum runs on Discourse (http://www.discourse.com/) which is a fantastic piece of software but requires either a significant investment of time in maintenance or quite a chunk of cash. They originally gave Hitmanforum a discount but that’s no longer sustainable and basically if we were to try to go back to them hosting and running everything for us - I’d need to negotiate a plan under the “Enterprise” section.
So instead, I run the software off a hosting cloud hosting service and do all the routine maintenance myself, including setting up to host image files on Amazon etc. At the moment it costs me $25 USD a month plus the damage to my brain caused by having to work out how to unix.
We used to use IP Board (https://invisioncommunity.com/) which offers a similar decision to make, it’s doubtlessly has changed a lot since last time I touched it but back in the day it was popular with people who liked coding because it had a lot of potential for forum “games” per se (giving you currency per post you can use to buy “items” kind of like Gaia) etc.
Even further back, in another life, I used to mod at places that used vBulletin (https://www.vbulletin.com/) which was a lot more business like but is still very functional and provides for discussion if you don’t mind the minimalist look (EN World, for example, still uses it).
And to be honest, if you’re just tossing something out to check the viability - phpBB (https://www.phpbb.com/) is free, easy to set up and quite functional even if it is widely mocked by people used to fancier forums that look more modern.
But all this depends on what you’re wanting - if you did want a specialist approach like say, a forum for speed runs where a new speed run gets announced and then people discuss it then WordPress might be the best solution.