iStat Menus - "An advanced Mac system monitor for your menubar."
Stats - Simple macOS system monitor in your menu bar.
iStatistica Pro - System monitor. Reinvented. 💻 🖥
MenuMeters for El Capitan - MenuMeters for OS X El Capitan 10.11 (and later)
Stats Panel - OS & Utilities, Network & Admin, and System & Hardware
Rooster - Local sharing community where neighbors share free resources