The FitbitGatt API is designed to provide a strong state machine around all Android gatt operations with the aim of making Android BLE development across Android vendors as straightforward and side-effect free as possible.
Build a Bluetooth GATT server with Android Things
Android Bluetooth Low Energy (BLE) Fast Development Framework. It uses simple ways to filter, scan, connect, read ,write, notify, readRssi, setMTU, and multiConnection.
A library that makes working with Bluetooth LE on Android a pleasure. Seriously.
An Android Bluetooth Low Energy (BLE) Library with RxJava2 interface