Pybytes (2.0) / Pybytes-legacy (1.0) is a cloud-based device management platform. You can use it to visualize the sensors data, see the status and geolocation of your devices and you can also perform Firmware Over the Air updates. Pybytes version 1.0 and 2.0 are built on top of the low-level firmware.
The legacy firmware contains the old low-level modules of the Pycom devices without pybytes. It contains the micropython interface, FreeRTOS and all the drivers (LTE, Wifi, Bluetooth, i2c, sockets, Lora, etc).