Qwiic is SparkFun's I2C prototyping system, it's only for use with I2C devices. There's also only one cable, a JST SH 4-pin connector and will only use it for I2C. Qwiic is a bit newer than Grove, it was created around May 2017.
- Like Qwiic, STEMMA only uses the 4-pin connectors for I2C. The STEMMA QT connector is identical to the Qwiic connector and uses the same pin ordering.
- Qwiic only has level shifting and voltage regulation on the controller, not devices. So, you can use STEMMA + STEMMA QT devices with any Qwiic controller and you can use Qwiic devices on a STEMMA controller if you set the voltage jumper from 5V to 3V (and have a cable that converts the 2mm to 1mm pitch connector)