This is just a pointer post to a tool which I discovered today. It is ORATOP, to monitor databases real time like top of unix flavours. It is pretty much like MOATS (tool from Tanel Poder and Adrian Billington and RAC version by Jagjeet Singh), with a bit better output (at least for my taste)
It doesn’t need anything to be installed which is the best part of the tool.
oratop – utility for near real-time monitoring of databases, RAC and Single Instance (Doc ID 1500864.1)
Sample output is like below. It can be a good addition to your performance tuning toolkits.
Coskan's Approach to Oracle 