Inspired by Theocritus's post, I'm listing here some resources to learn Ancient Greek in Ancient Greek:
Διονυσίου τοῦ Θραικὸς τέχνη γραμματική
Theodosii Alexandrini Grammatica
Γραμματικὴ Κωνσταντίνου Λασκάρεως
Ἡ κατ'ἐπιτομὴν γραμματικὴ ὑπὸ Νεοφύτου Δούκα.
Do you have more to suggest? I limited myself to books printed in the XIX century and later, since I found more complex ligatures in earlier books hard to decipher.