Welcome to the new forum. As you can see we’ve upgraded from phpBB to Discourse. Discourse is an open source modern forum. It seems very responsive and has tons of features. If any of the features need tweaking or seem superfluous or if there is anything weed can add with extensions/add-ons let us know in the #site-feedback category. More info on Discourse can be found @ https://meta.discourse.org/categories.
That is the most obvious difference difference I have noticed. Discourse uses categories for forums/subforums.
Also you should have a message in your inbox from our friendly neighborhood @discobot. If you reply to him he will show you around.