DFRobot has their own plug-n-play system as well, called Gravity. It's a little less well defined than Grove/Qwiic, but it seems to use 3-pin JST's for digital/analog and 4-pin JST's for I2C/UART. Other than the UART 4-pin devices, Gravity and STEMMA are compatible with each other.
- STEMMA 4-pin parts and cables are cross-compatible with Gravity I2C parts. You can plug the larger 4-pin STEMMA cables/devices/controllers into Gravity I2C devices/controllers just fine and vice-versa. UART won't work because STEMMA is for I2C only.
- STEMMA 3-pin parts and cables a are also cross-compatible. You can plug 3-pin STEMMA cables/devices/controllers into Gravity analog/digital/PWM devices/controllers just fine and vice-versa.
- STEMMA uses the same voltage as Gravity - power is 3-5VDC and data is 3-5VDC with level shifting/regulators on devices.
- Some Gravity devices use 4-pin connectors for non-I2C data like UART. STEMMA only uses I2C for the 4-pin connectors.