Using Grbl's Spindle PWM to Control a Servo at Buildlog.Net Blog
LaserWeb for EggBot: I slightly modified Grbl to be used with a servo instead - LaserWeb/CNCWeb - Maker Forums
Grbl1.1 Controller Board 2axis Stepper Motor Control Double Yaxis Support Servo For Grbl Laser Engraving Machine - Woodworking Machinery Parts - AliExpress
Motion Control / Positioning Control for PLC using Arduino :
How to Make GRBL + CNC V3 Shield Based Mini CNC - Hackster.io
GitHub - robottini/grbl-servo: grbl 0.9i with Servo motor support
GitHub - bdring/Grbl_Pen_Servo: Grbl CNC Controller with Pen Servo Feature