Neat. A couple thoughts:
1) it took me some time to figure out that I could scroll a given column when the mouse is over it... Also when the mouse is over a non-column area (background on far right/left) it would be useful if scrolling did a global scroll of all columns at the same time.
2) It could be nice if the sections M+1/M-1 (above/below) the selected section in column N were given a subtle distinct color, and then the appropriate sections in column N+1 that are nested in M+1/M-1 were given the same color. Does that make any sense? It would give a visual indication of which sections in column N+1 lie within sections M+1 and M-1, and also help to emphasize the tree nature of the layout. A different color could be chosen for M+/-2, +/-3, etc.
We explored having different color scheme to denote the node distance between two cards.
Unfortunately, it got too messy, and neither of us are designers, so we had to shelve it for now.
As for scrolling, and want the mouse scrolling to work just like keyboard (selects the card at center, reorders other columns appropriately). Haven't gotten around to it yet.
2) It could be nice if the sections M+1/M-1 (above/below) the selected section in column N were given a subtle distinct color, and then the appropriate sections in column N+1 that are nested in M+1/M-1 were given the same color. Does that make any sense? It would give a visual indication of which sections in column N+1 lie within sections M+1 and M-1, and also help to emphasize the tree nature of the layout. A different color could be chosen for M+/-2, +/-3, etc.
Good job! :)