Any app or script to track per process usage?

You could also use a shell command like this:

while :;do ps -p 1234 -o %cpu=;sleep 1;done

Replace 1234 with the pid of the process.

You can use gnuplot to create a graph for the data:

gnuplot<<<'set term png;set output "/tmp/plot.png";plot "/tmp/data" with boxes'
qlmanage -p /tmp/plot.png

Based on answer from Lri,

MacOS solution to create the following graph

# Install dependencies
brew install gnuplot libmagic 

# Sample process. Replace 1234 with process ID
while sleep 1;do ps -p 1234 -o %cpu= >> procdata.txt;done

# Plot
gnuplot<<<'set term png;set output "procplot.png";plot "procdata.txt" with boxes'