B-Eng has launched System Bar (http://www.b-eng.ch/app/system-bar/), a low impact system monitoring utility for macOS. It shows the main system information at a glance in a single bar, that can be freely customized and positioned anywhere on the screen.
Colors, size and fonts are freely adjustable. The utility shows the time on an analog clock face, CPU usage, used memory and available disk space. A right click reveals the top resource heavy CPU processes and grants direct access to the Activity Monitor. System Bar requires macOS 10.12 and costs $1.99.