This is my contribution to the excellent OTN Appreciation Day idea by Tim

The Flashback (particularly Flashback Query) features of the database have saved my neck many (too many!) times over the years.

For example retrieving the value of the Employees salary as it was 10 minutes ago:

SQL> select sal 
 from emp 
 as of timestamp sysdate - interval '10' minutes 
 where ename = 'SCOTT';

This feature can be used almost everywhere Oracle is used, for example it’s embedded into the Export Application feature of Oracle Application Express

As an extension to this, using the Flashback Data Archive feature allows you maintain an archive  of your application data that you can query in real time – without having to write your own logic.

Flashback – an extremely useful but often little known and underused feature of Oracle!