Here are brief descriptions of SQLFire classes and interfaces, with links to the JavaDoc and pertinent user guide sections.

SQLFire Class or Interface Description
AsyncEventListener Provides a mechansim to receive callbacks on execution of DML (Create,Update,Delete) statements in SQLFire. Use an AsyncEventListener to analyze data and take desired actions such as persisting data in a specific format.

To do this, you create a class implementing the AsyncEventListener interface. The callback method processEvents(List<Event> events) processes information related to manipulated rows, such as new values. An AsyncEventListener instance is serviced by its own dedicated thread in which a callback method is invoked. Events corresponding to DML are placed in an internal queue and the dedicated thread dispatches a batch of events at a time to the user-implemented callback class, the frequency of which is governed by the configuration of the AsyncEventListener.

DBSynchronizer Built-in AsyncEventListener used to asynchronously persist data to a third- party JDBC 4.0-compliant RDBMS. The steps for configuring DBSynchronizer are the same as those for configuring AsyncEventListener. Using DBSynchronizer to Apply DML to an RDBMS describes the process.
Event Provides information about the row inserted, updated, or deleted using the callback mechanism. The callback itself can be registered either through CacheListener or AsyncEventListener. How the AsyncEventListener Works provides more information.
EventCallback Interface to be implemented by synchronous cache plug-ins (writers and listeners). Handling DML Events Synchronously and the JavaDoc provide more information about implementing this interface.

SYS.ADD_LISTENER shows a sample implementation.

FabricLocator Singleton that provides locator services in the distributed system that allow peers to discover one another.
FabricServer Enables an application process to join the SQLFire cluster either as a data store by hosting data or as an accessor (peer client) to the real data.
FabricServiceManager Facilitates acquiring a FabricServer or FabricLocator instance. A virtual machine can be booted as either a FabricServer or a FabricLocator but not both.
NetworkInterface Clients can connect to a NetworkInterface using the SQLFire JDBC client driver (URL of the form 'jdbc:sqlfire://<host>:<port>'). Network listener instance can be acquired by invoking FabricServer startNetworkServer method. SQLFire uses DRDA protocol for client-server communication. Starting a Network Server provides an example of creating a network listener.
RowLoader Invoked when a SELECT query is executed against a table with a WHERE clause that includes an equals (=) test for every component that is part of the table's primary key and an entry for that primary key does not exist in memory. Using a RowLoader to Load Existing Data provides more details.
OutgoingResultSet This interface is used when implementing data-aware-procedures, to construct an outgoing result set by adding rows as a List<Object>.