What has the author Barnabas written?

There is no known author named "Barnabas" who has written any notable works.

It's possible you're thinking of:

* The Epistle of Barnabas: This is an early Christian writing from the 1st or 2nd century, often attributed to a figure named Barnabas (though this is debated). However, there's no definitive proof of the author's identity.

* Barnabas (Apostle): This is a figure mentioned in the New Testament, a close companion of the apostle Paul. He wasn't known for writing books.

Could you clarify your question or provide more information?