The basic requirement was to build a blind-typing chording keyboard for individual use. The proposed design should be for a desktop use (not a handheld) and should allow reasonably fast data entry for programming languages and common text entry. All function keys and their combinations with Alt, Control, Shift, Win should be supported. Additionally, the keyboard must support 2nd language entry with Cyrillic alphabet.

The basic conceptual design:

• 3 keys under the left thumb are used as Alt, Control, and Shift.
• 2 keys under the right thumb are "Fun" and "Num" -- used for inputting numbers and functions keys. The last key at the left thumb is a Space.
• 8 keys under the other fingers are used for the "chorded" input:

Here the fingers are recorded as PRMI-IMRP: Pinky, Ring, Middle, Index

1. Eight letters from one-key inputs, as suggested by ASETNIOP
2. Twenty-six letters from two-key inputs, but unlike ASETNIOP, combinations PM and MP are not used. Personally I have trouble lifting the ring whilst pressing the middle and the pinky. The BAT keyboard explicitly avoided such combinations. Together with the single-finger buttons, this gives 34 combinations, sufficient for both Russian and Ukrainian scripts.
3. Several three-key and four-key combos are used for the punctuation marks, carefully avoiding the PM, MP, PMI, and IMP.

A mockup was built, first with cardboard, then with chipboard. The latter served also for the initial prototype testing. The keycaps were held in place with two-sided scotch. For my rather short fingers, the optimal horizontal spacing seemed to be 30mm, the hand angle -- 40 degrees.