Track per-device volume for Bluetooth media devices. For whatever reason on my Pixel 2, every time a headset/speaker/whatever connects, its volume is reset to some default amount. This app remembers the last volume it saw for a device and restores that volume whenever that device reconnects.
This app is for Oreo and up; I haven't done the compatibility thing for older OSes because, well, I wrote it for my Pixel 2.
In principle, it should be possible to check the volume level as the device is disconnecting and store that. However, the CONNECTION_STATE_CHANGED action occurs too late, after the volume has already reverted to the internal speaker. So, instead, while an A2DP device is connected, there's a foreground service that receives MediaRouter callbacks on volume changes. It's a bit regrettable and I might eventually make this an option with a manual sync button.
UPDATE: Pie finally incorporates this behavior, so this app is more or less useless. :)