Author of terminal file manager nnn here. I have released v3.2 of the utility today. It brings some interesting new features like preview hovered, find subtree & list, persistent sessions etc.
While I was making the release I realized that the FIFO implementation (for previews) may not work as it is on Haiku. Also, we have introduced some icons for desktop users. The location may be different on Haiku.
Our regular maintainer is busy and away for a while. Would someone be interested in porting the changes? I will be glad to make a minor release when it is ready to deploy on Haiku.
All the best!