Not sure what you mean re. Rails, not to mention testing in Rails is far easier. As far as the modify part goes, I definitely agree XenForo is far easier to modify, but I think that goes both ways. Forums bloated with extra plugins are just confusing to operate and unfamiliar for users. Whilst some webmasters may enjoy spicing their site up with 60+ add-ons, from a user's standpoint, it isn't always so great. I lurk in a few communities that use Discourse and I enjoy how familiar each of those are to the other - there's very little customisation and things are exactly where I expect them to be. For most sites that use Discourse, visible customisation is not really a core requirement.Xenforo is more advanced. Discourse is good for mobile devices and it's fast, but xenforo has a lot more functionality, easier to modify, has more addons that are easier to maintain. Discourse uses ruby on rails which is a nightmare to maintain without breaking the whole site.