"Tamil Olu Kathai" seems to be a term in Tamil, and when translated, it roughly means "Tamil Writing" or "Tamil Script". If you're looking for useful texts or resources related to Tamil writing or learning Tamil, here are a few suggestions:
The Olu Kathai mirrors the concept of Naadham (primal sound) in Hinduism. Just as the Om sound created the universe, the Olu in a story creates the narrative universe. Temples like Chidambaram (Nataraja Temple) are based on the concept of Akasa Bhootham (space/sound ether), which resonates with the "echo" theme in these stories. Tamil Olu Kathai
Project Gutenberg: While not extensive, Project Gutenberg has a few Tamil eBooks that you can download for free. "Tamil Olu Kathai" seems to be a term
Tamil Virtual Library: This is a digital library that provides access to Tamil literature. It includes works from various genres and periods. For Tamil Literature:
Google Books: There are many scanned books available on Google Books, including works of Tamil literature.