Numerical digit
From India, the thriving trade between Islamic sultans and Africa carried the concept to Cairo. Arabic mathematicians extended the system to include decimal fractions, and Muḥammad ibn Mūsā al-Ḵwārizmī wrote an important work about it in the 9th  century. The modern Arabic numerals were introduced to Europe with the translation of this work in the 12th century in Spain and Leonardo of Pisa's "Liber Abaci" of 1201. In Europe, the complete Indian system with the zero was derived from the Arabs in the 12th century.
History of the Arabic alphabet
Since the early 20th century, as the Ottoman Empire collapsed and European influence increased, many non-Arab Islamic areas began using the Cyrillic or Latin alphabet, and local adaptations of the Arabic alphabet were abandoned. In many cases, the writing of a language in Arabic script has become restricted to classical texts and traditional purposes (as in the Turkic States of Central Asia, or Hausa and others in West Africa ), while in others, the Arabic alphabet is used alongside the Latin one (as with Jawi in Brunei).