undocumented commands in Oracle (for DBA)

Are there any undocumented commands in Oracle? (for DBA)
Sure there are, but it is hard to find them. Look at these examples:
From Server Manager (Oracle7.3 and above): ORADEBUG HELP
It looks like one can change memory locations with the ORADEBUG POKE command. Anyone brave enough to test this one for us? Previously this functionality was available with ORADBX (ls -l $ORACLE_HOME/rdbms/lib/oradbx.o; make -f oracle.mk oradbx) SQL*Plus: ALTER SESSION SET CURRENT_SCHEMA = SYS

If the maximum record retrieved property of the query is set to 10 then a summary value will be calculated?
Only for 10 records.

What are the different objects that you cannot copy or reference in object groups? 
Objects of different modules
Another object groups
Individual block dependent items
Program units.

What is an OLE? 
Object Linking & Embedding provides you with the capability to integrate objects from many Ms-Windows applications into a single compound document creating integrated applications enables you to use the features form .

Can a repeating frame be created without a data group as a base? 
No

Is it possible to set a filter condition in a cross product group in matrix reports? 
No

What is Overloading of procedures ? 
The Same procedure name is repeated with parameters of different datatypes and parameters in different positions, varying number of parameters is called overloading of procedures. e.g. DBMS_OUTPUT put_line

What are the return values of functions SQLCODE and SQLERRM ? What is Pragma EXECPTION_INIT ? Explain the usage ? 
SQLCODE returns the latest code of the error that has occurred.
SQLERRM returns the relevant error message of the SQLCODE.