(new york, ny)
The plant leaves are about the size of a pinky nail, generally firm, slightly squishy when over watered, and bright green. You can see darker green lines in the leaves themselves. Grows on stems in little clusters, in a bush like formation. Shallow roots.
I bought it in December, from the NY Botanical Gardens. Haven't seen it on any website or nursery since then.
These aren't unknown, they're just not that common - or, usually, they go under the wrong name and fly under the radar.
Haworthia (which have no common name) are unusual little characters; they actually prefer a bit more water, and also will grow best in a bit less bright light.
Lots of times, they are bunched in with other types of succulents like Aloe, but if you try and grow them in the hot and bright conditions that those plants prefer, they will suffer with it, and finally give up the ghost.
You can see more about these great little plants here: Haworthia; yours looks like Haworthia cymbiformis or a hybrid of that species.