BitBar - Put anything in your Mac OS X menu bar
iStat Menus - "An advanced Mac system monitor for your menubar."
SwiftBar - Powerful macOS menu bar customization tool.
Stats - Simple macOS system monitor in your menu bar.
MenuBar Stats - Advanced Mac system monitor right from the menu bar
AnyBar - AnyBar is a small indicator for your menubar that does one simple thing: it displays a colored dot. What the dot means and when to change it is up to you.