What writing systems do you know

[Jipí]

Balinese and Javanese also use subscript consonants and have some diacritics for common codas (IIRC e.g. -n)

[Mornche Geddick]

Latin alphabet and Pitman's shorthand. The Greek alphabet, but not the digraphs and diacritics.

[BloodMerchant]

Latin, Greek, Japanese, Chinese, Cyrillic

I'm still learning Armenian, Georgian, Aramaic-Syriac and a few Brahmic scripts.