You can download the library at GitHub.
Here is a video.
Here is another video, showing the Joy-Con repurposed as a control mechanism for the HoloPlayer One.
Some brief technical details about the Joy-Con hardware follow:
The Joy-Con pushes raw HID packets over Bluetooth every 15 ms; the HD Rumble motors are likely manufactured by ALPS under the HAPTIC Reactor brand name. Every 15ms the HD Rumble motors can be updated with a high and low frequency and amplitude for each.
The accelerometer / gyroscope is an LSM6DS3 by STMicroelectronics. It is a 6-axis sensor and contains no magnetometer, so it can only calculate an absolute yaw value. My library includes a Recenter method, which sets the Joy-Con yaw value to zero.
This project would not exist without the work of dekuNukem, mfosse, and CTCaer. The Unity HID code was built on Signal11's cross-platform hidapi, with bits of wrapper code copied from Unity-Wiimote. My sensor fusion code is heavily based on the excellent Direction Cosine Matrix tutorial from Starlino.
This library is a work in progress - if you want to build a Unity project that uses the Joy-Con and have questions, feel free to submit an issue on Github.