On this chart one can see the origins of both the Brahmi related Siddham texts which is very important to Vajrayana Buddhism and the Runic Alphabet which are important to Celto-Germanic peoples. Their relations to very important writings like Greek, Cyrillic, are vey important to understand as well.
One thing I think is missing from this chart is the influences of Cuneiform. As well as Turkic and Germanic Runes.