An older app that is similar is The Brain. It allows you to move in and out of topics and does a decent job of dealing with large numbers of items. I used it a

An older app that is similar is The Brain. It allows you to move in and out of topics and does a decent job of dealing with large numbers of items. I used it a lot in the early 2000s and it's still around. https://www.thebrain.com/ https://www.thebrain.com/