RTGP is a simple implementation, forwarding ROOT histogram information to gnuplot, to plot it to the command line.
The original rtgp is still here
Wrapping all in
gnuplot-iostream seemed a bit
more elegant - although … it also just does a syscall - using popen instead
of system. And more recently I also saw how to use temporary files
here
linked from
here
The (in my eyes) greatest disadvantage is that the gnuplot-iostream approach depends on boost libraries which caused an incredible amount of trouble in all of my projects (counter intuitive syntax and -worse- breaks whenever moving to a new computing cluster, compiler version, operating system).
For now the system loads are:
gSystem->Load("path/to/libboost_system.so");
gSystem->Load("path/to/libboost_iostreams.so");
gSystem->Load("path/to/librtgp.so")
See the video here demonstrating how rtgp looks in action.

