gfxcardstatus

Install command: 
brew install --cask gfxcardstatus

Name: gfxCardStatus

Menu bar app to monitor graphics card usage

https://gfx.io/

Cask JSON API: /api/cask/gfxcardstatus.json

Cask code: gfxcardstatus.rb on GitHub

Current version: 2.5

Requirements: macOS >= 10.11

Analytics:

Installs (30 days)
gfxcardstatus 50
Installs (90 days)
gfxcardstatus 170
Installs (365 days)
gfxcardstatus 572