The best tool I've ever used for this no longer exists, as far as I'm aware. It was circa 1991, a spectacular lightweight Macintosh application called "Inspiration." There currently exists software in the same lane with the same name - but if there's any blood relation between the two, the current bears little resemblance to its progenitor.
I will mangle the terminology since it's been so long, but the basic idea was that on an infinite canvas you would create nodes representing concepts; these nodes were just UI "bubble" objects, like the ovals you might find in slide deck software. Relationships could be added after the fact by linking these nodes, and there was a fast way to create linked "sub-nodes" from an existing node. Also, very strong UI for arranging the node diagram.
Maybe the big problem with mind mapping tools these days is feature creep. A complex UI with too many options will absolutely get in the way of the thought process it serves.