The OpenNTF Domino API is a community-developed Java API that provides an alternative to using the native Notes objects in Domino. It was created to bridge the gap between LotusScript and Java developers, remove the need for try/catch blocks and recycling, and take advantage of Java collections and helper methods. The API is deployed via an update site and its packages include core interfaces, extension interfaces, and implementation classes. It provides features like logging, transaction processing, and database event listeners. Developers can convert code by changing imports, removing unnecessary code, and using the API's helper methods.