What Oobly said.
TypeMatrix and many point-of-sale keyboards (e.g., Access-IS, Tipro, Elcom, Cherry G80-1950 and some G86s) have a matrix/grid layout. Humble Hacker Keyboard and GH36 DIY projects are like that as well.
Most actual ergonomic keyboards don't really have a strictly matrix layout, because the columns are usually vertically staggered to correspond to finger length (that isn't uniform), at least partially. Sometimes, the key wells are curved to achieve the same thing (I mention this, because Kinesis Advantage has almost a matrix layout with separate thumb clusters, but the matrix isn't flat).
Then there are a few keyboards with a symmetrically staggered layout, especially the μTRON.
I think there are several distinct features of mentioned layouts:
- symmetrical (hands are generally symmetrical)
- split/curved/row-staggered (shoulders are about 46 cm wide on average; if you put your hands in parallel, matrix/columnar layout usually feels natural, but if your hands form a triangle, the keyboard halves need to be positioned to compensate for that… or maybe row staggering might help a bit)
- straight columns (eliminate most lateral finger movements)
- column-/depth-staggered (compensate for inconsistent finger length, but it's usually one-size-fits-all, unfortunately)
- thumb clusters (because of thumb opposition)