Au (Indic)
Au is a vowel of Indic abugidas. In modern Indic scripts, Au is derived from the middle "Kushana" Brahmi letter , and the Gupta letter . As an Indic vowel, Au comes in two normally distinct forms: 1) as an independent letter, and 2) as a vowel sign for modifying a base consonant. Bare consonants without a modifying vowel sign have the inherent "A" vowel. Āryabhaṭa numeration

Aryabhata used Devanagari letters for numbers, very similar to the Greek numerals, even after the invention of Indian numerals. The  ौ sign was used to modify a consonant's value , but the vowel letter औ did not have an inherent value by itself. Historic Au
There are three different general early historic scripts - Brahmi and its variants, Kharoṣṭhī, and Tocharian, the so-called slanting Brahmi. Au was not found in the earliest forms of Brahmi, but was found in the more flowing forms the Kushana  and Gupta . Like all Brahmic scripts, Tocharian Au  has an accompanying vowel mark for modifying a base consonant. In Kharoṣṭhī, the only independent vowel letter is for the inherent A. All other independent vowels, including Au are indicated with vowel marks added to the letter A.

Brahmi Au
The Brahmi letter Au, is based on the letter O which was probably derived from the  Aramaic Waw . That would make it related to the modern Latin F, V, U, W, Y and Greek Upsilon. Several identifiable styles of writing the Brahmi Au can be found, most associated with a specific set of inscriptions from an artifact or diverse records from an historic period. As the earliest and most geometric style of Brahmi, the letters found on the Edicts of Ashoka and other records from around that time are normally the reference form for Brahmi letters, but only being found in later styles, the reference form of Brahmi Au is back-formed from later styles to match the geometric writing style. Tocharian Au
The Tocharian letter  is derived from the Brahmi . Unlike some of the consonants, Tocharian vowels do not have a Fremdzeichen form. Kharoṣṭhī Au
The Kharoṣṭhī letter Au is indicated with the O vowel mark  plus the vowel length mark . As an independent vowel, Au is indicated by adding the vowel marks to the independent vowel letter A . Devanagari Au

Au (ओ) is a vowel of the Devanagari abugida. It ultimately arose from the Brahmi letter , after having gone through the Gupta letter . Letters that derive from it are the Gujarati letter ઔ, and the Modi letter 𑘍.

Devanagari Using Languages
The Devanagari script is used to write the Hindi language, Sanskrit and the majority of  Indo-Aryan languages. In most of these languages, ओ is pronounced as . Like all Indic scripts, Devanagari vowels come in two forms: an independent vowel form for syllables that begin with a vowel sound, and a vowel sign attached to base consonant to override the inherent /ə/ vowel. Bengali Au

Au (ঔ) is a vowel of the Bengali abugida. It is derived from the Siddhaṃ letter , and is marked by the lack of horizontal head line and less geometric shape than its Devanagari counterpart, ओ.

Bengali Script Using Languages
The Bengali script is used to write several languages of eastern India, notably the Bengali language and Assamese. In most languages, ঔ is pronounced as . Like all Indic scripts, Bengali vowels come in two forms: an independent vowel form for syllables that begin with a vowel sound, and a vowel sign attached to base consonant to override the inherent /ɔ/ vowel. Gujarati Au

Au (ઔ) is a vowel of the Gujarati abugida. It is derived from the Devanagari Au , and ultimately the Brahmi letter . Gujarati-using Languages
The Gujarati script is used to write the Gujarati and Kutchi languages. In both languages, ઔ is pronounced as . Like all Indic scripts, Gujarati vowels come in two forms: an independent vowel form for syllables that begin with a vowel sound, and a vowel sign attached to base consonant to override the inherent /ə/ vowel. Javanese Au

Telugu Au

Au (ఔ) is a vowel of the Telugu abugida. It ultimately arose from the Brahmi letter . It is closely related to the Kannada letter ಔ. Like in other Indic scripts, Telugu vowels have two forms: and independent letter for word and syllable-initial vowel sounds, and a vowel sign for changing the inherent "a" of Telugu consonant letters. Vowel signs in Telugu can interact with a base consonant in one of three ways: 1) the vowel sign touches or sits adjacent to the base consonant without modifying the shape of either 2) the vowel sign sits directly above the consonant, replacing its v-shaped headline, 3) the vowel sign and consonant interact, forming a ligature. Malayalam Au

Au (ഔ) is a vowel of the Malayalam abugida. It ultimately arose from the Brahmi letter , via the Grantha letter  au. Like in other Indic scripts, Malayalam vowels have two forms: an independent letter for word and syllable-initial vowel sounds, and a vowel sign for changing the inherent "a" of consonant letters. Vowel signs in Malayalam usually sit adjacent to its base consonant - below, to the left, right, or both left and right, but are always pronounced after the consonant sound. Odia Au

Au (ଔ) is a vowel of the Odia abugida. It ultimately arose from the Brahmi letter , via the Siddhaṃ letter  au. Like in other Indic scripts, Odia vowels have two forms: an independent letter for word and syllable-initial vowel sounds, and a vowel sign for changing the inherent "a" of consonant letters. Vowel signs in Odia usually sit adjacent to its base consonant - below, to the left, right, or both left and right, but are always pronounced after the consonant sound. No base consonants are altered in form when adding a vowel sign, and there are no consonant+vowel ligatures in Odia. Kaithi Au

Au (𑂌) is a vowel of the Kaithi abugida. It ultimately arose from the Brahmi letter , via the Siddhaṃ letter  Au. Like in other Indic scripts, Kaithi vowels have two forms: an independent letter for word and syllable-initial vowel sounds, and a vowel sign for changing the inherent "a" of consonant letters. Vowel signs in Kaithi usually sit adjacent to its base consonant - below, to the left, right, or both left and right, but are always pronounced after the consonant sound. No base consonants are altered in form when adding a vowel sign, and there are no consonant+vowel ligatures in Kaithi. Comparison of Au
The various Indic scripts are generally related to each other through adaptation and borrowing, and as such the glyphs for cognate letters, including Au, are related as well. Character encodings of Au
Most Indic scripts are encoded in the Unicode Standard, and as such the letter Au in those scripts can be represented in plain text with unique codepoint. Au from several modern-use scripts can also be found in legacy encodings, such as ISCII. 