System Monitor Pro

It has 2 main options:

It can record on a CSV file the read values for a later usage and process on a spreadsheet program.
The app can run in the background. Then, the second option is specially interesting since, in the background, AnotherMonitor consumes little resources and can monitor and record the CPU and memory values that other applications are using in the foreground.

The app can be closed, and the recording of values can be started from the buttons shown in the system bar.

In order to get the CPU usage the app does not make use of the Top command from Linux but instead it parses the /proc/stat file and work out the calculatios with the user and system time.