From the users view, domingo is a set of interfaces together with a factory class to create instance classes of the interfaces to access Lotus Notes/Domino.
There are currently two implementations of the interfaces: the single-threaded proxy-implementation encapsulates the Java-API of Notes and contains work-arounds for many problems and bugs. The multi-threaded service-implementation provides a thread pool to simplify thread handling when using local calls to a Notes-Client. A third implementation is under development that uses HTTP und XML/DXL to access Domino servers.
Furthermore, a resource adapter is under development allowing access to Lotus Notes/Domino in an EJB-Container.
For any further information please read the JavaDoc of domingo