Gambal is a tiny transparent window that provides an overview of network, CPU and memory usages.
It's light-weight and uses libX11 for GUI and should work on all distros.

There are .deb and .rpm packages for different atchitectures in latest release page.

If you are on Arch linux and xorg-fonts-misc package is not installed. install it and logout and login to your desktop.

sudo apt-get install build-essential cmake libx11-dev
git clone https://github.com/ashtum/gambal.git
cd gambal
mkdir build
cd build
cmake ..
sudo make install
sudo gtk-update-icon-cache /usr/share/icons/hicolor

mouseover appears options, change network interface by click on < and > buttons.
click and drag moves window.
mouse middle-click toggles font style.
mouse wheel up/down changes window opacity.
right click exits application.