Oscan was an Italic language related to Latin, which died out somewhere in the early centuries CE. It's notable for being used in the Fabulae Atellanae and for being the source of various loans into Latin, such as lupus "wolf".
To the best of my understanding (based on Buck's grammar), nine of the ten Proto-Italic vowels are distinguished in the Oscan orthography:
ī i ē e a ā o ō u ū
𐌉𐌝 𐌝 𐌝𐌝 𐌄 𐌀 𐌀𐌀 𐌞 𐌖𐌖 𐌖 𐌖𐌖
(In other words, ō merged with ū, and the rest were distinct, in the idealized perfect writing system where all long vowels are marked and no errors are made.)
The interesting part, though, is how this shows the different vowel qualities. It seems like ē was closer in quality to i than either was to e or ī, for example, foreshadowing later developments in Romance.
But I'm curious: were there any more vowel qualities than the six letters could show? For example, did transcriptions into the Greek alphabet (which had more letters available) distinguish the reflexes of ō from ū, or were they truly identical?