FluxBB is a fork of PunBB, which is why I usually group these two together when talking about them. They're both lightweight forum software, that are perfect for those who want a fast loading community alongside a blog or main website. Since they're lightweight, most of the common forum features such as a private messaging system doesn't come with the software out of the box. Instead you have to install plugins to get other features that most software already has. The team behind FluxBB has basically moved on to flarum, which is more of a modern forum platform however. I think some of the developers are still slowly working on FluxBB, as for PunBB the latest update came out early 2021 so it's still being maintained. Have you ever used either software for your communities? I've tried FluxBB out before, but I wanted a bit more from my community at the time so I switched to MyBB eventually before shutting the project down.