I am not sure that there exists a BAPI to see list of all BAPI’s in SAP system. You can use the Function module RFC_FUNCTION_SEARCH to search for function modules starting with BAPI*.
You can call Function Module-BAPI_MONITOR_GETLIST to get list of all available BAPI’s.
CALL FUNCTION'BAPI_MONITOR_GETLIST' EXPORTING OBJECTTYPE = p_ojtpe SHOW_RELEASE = p_rel BAPIS_POTENTIAL = p_poten BAPIS_NEW = p_new_pabi BAPIS_OLD = p_old_bapi RELEASED_BAPI = p_rel_bapi RELEASED_FUNC = p_released_func IMPORTING RETURN = d_ret TABLES COMPONENTS2SELECT = int_cs SYSTEMS2SELECT = int_sss BAPILIST = int_bapilist
There exists a Function module - RFC_READ_TABLE, this can be used for external access to SAP R/3 system via RFC.
Using this, you could read table DD02L to get the tables in the system.