Activity monitor is not always good if you want to see what is keeping your computer busy for a period of time.
For example if you have gcc executed hundred of times it will take a lot of CPU power but the overall CPU time consumed by gcc will not appear. I'm looking for a solution that is able to count and summarize application usage so I can know that how the cpu was used.
Best Answer
I'm a huge fan of Bjango's iStat menus, which allows one to conveniently place various monitors (CPU, disk usage, network up & down, battery, memory, temperature sensors...) up in the menu bar. Each one can be pulled down like a menu for additional details. It's a $16 app. You can try before you buy.
Edit: it looks like they have released another monitoring application called MiStat that is a separate app instead of living in the menu bar. This allows them to place it in the Mac App Store. It's available for a $4.99.
Edit: I'm sorry, I must have not read your question carefully enough before I posted. I do not know of any GUI tool that is able to aggregate CPU time being consumed by several similar processes as you describe. The best idea that I can think of would be to write a script that wraps the top or ps commands and adds up processes that match a regular expression. This strikes me as a market opportunity for a nice utility. Could you describe a little more of how you would like such a thing to behave?