MyDBA - Oracle Databases Observer - description from Softdepia.com:
MyDBA is a powerful graphical tool to retrieve essential information from any Oracle database. Quickly detect potential problems in your databases. In addition to all functionalities of the program you can create and store in it your own DBA scripts and automatically run them at your convenience. Customizable real-time statistics, automatically refreshed screens, customizable thresholds. Also nice for DBAs beginners. Shipped with installer and uninstaller.
MyDBA - Oracle Databases Observer is a "Free to try" program. You can download and try it for an evaluation period.