NeO outliner by d-lit forums/users
I don't know of any place specifically to discuss Neo, but I've been using it for a few years (used to be called Tao) and it is my most used application on my computer. I own licenses for Neo and OmniOutliner and Neo is just much much much more configurable and powerful. It has a bit of a learning curve, but it's an amazing piece of software. In the Windows world I used to use Ecco Pro, which is also amazing and free nowadays.