[bvdxcvhg] Four-finger keyboard

Four buttons: A or B are pressed by the thumb (or neither, but not both), and C and D are pressed by the other fingers.   There are 11 chords.

A
B
C
D
AC
AD
BC
BD
CD
ACD
BCD

The 7 chords can be arpeggiated in each of two ways (arpeggios starting or ending in the middle are too weird), giving 18 total.  If we arpeggiate the release as well, that gives 25 total, one short of the number of letters, and many short including space and punctuation.

Inspired by the stenotype machine.