Baybayin is a pre-Spanish Philippine writing system, it is a member of the Brahmic family and is recorded as being in use in the 16th century.
The term Baybay literally means “to spell” in Tagalog. Baybayin was extensively documented by the Spanish. Some have attributed it the name Alibata, but this name is incorrect.
Baybayin is one of a number individual writing systems used in Southeast Asia, nearly all of which are abugidas where any consonant is pronounced with the inherent vowel a following it — diacritical marks being used to express other vowels (this vowel occurs with greatest frequency in Sanskrit, and also probably in all Philippine languages).
Above: The word Tumblr in Baybayin post-kudlit form.