Lets you somewhat control SoundCloud using Android Auto. Does not support playlist switching or browsing, pretty much all it does is hook up the previous/next buttons in your car to the SoundCloud app.
There is NO WARRANTY provided with this app. If using it causes Android Auto to break and navigate you off a cliff into the ocean, don't blame me. If you use this to blast anime music out your car and everyone finds out that you're a weeb, AGAIN, NO WARRANTY. That said, I've been using this for a few months now with no issues (well, except for the anime part), but still - NO WARRANTY. NONE. NIL. ZERO.
First, enable developer settings in the Android Auto app (please figure this out on your own, I'm not going to help you shoot yourself in the foot). Once that's done, enable unknown sources in the developer settings menu. Cardapter should now be visible in Android Auto.
Unfortunately, SoundCloud does not (to my knowledge) export information about your playlists, so if you want to switch between e.g. liked/stream, you have to use the actual SoundCloud app to start playback. Once playback is started you can seek between tracks using the normal Android Auto controls.
Note that for some reason Android Auto doesn't like to jump directly to the now playing view; you may have to manually press the blue circle to pull that up. This is probably fixable, but I haven't found the time to investigate why this happens. Please submit a pull request if you can figure this out.
SoundCloud has a neat little component that exports the playing state, which I presume it uses for the media notification. Funnily enough, all it would take to get the exact behavior as this app in the real SoundCloud app would be to add a 4-line XML file:
<?xml version="1.0" encoding="utf-8"?>
<automotiveApp>
<uses name="media" />
</automotiveApp>
This app effectively acts as a wrapper for the real app that adds this XML file.