A Mongolian abugida.

Collection of encrypted correspondence between the compiler and various correspondents, in approximately 150 alphabets, accompanied by transcriptions of the letters in Arabic. The compiler cites Shihāb al-Dīn al-Jindī al-ʻAlāʼī, Burhān al-Dīn al-Qudsī, and Taqī al-Dīn Muḥammad ibn Jaʻfar al-Ḥusaynī as authorities for some of the alphabets. The manuscript is incomplete, lacking its beginning and end. Occasional marginal notes. Some worm damage in margins.

Via https://t.me/linguopunk/549

Арабская книга 14 века с собственным тайным алфавитом для тайных записей

Хорошее введение в иероглифы. Я это всё знал, что показывает совсем уж входной уровень материала, но интересно всё равно.

gesture - handwriting algorithm with implementation for linux touchscreens injecting keys into a tty.