Not fully open source,
but less proprietary crap.

AA4MG (Android Auto 4 MicroG)

It allows to run Android Auto with:

• MicroG, open source alternative to Google Play Services)
• Empty stub APKs, for the other Google Android Auto dependencies (e.g. Google Maps, TTS Text To Speech, …)

That way the only proprietary thing you need,
is the actual Android Auto app,
not it’s hand full of sketchy propriety dependencies.

Full disclosure: I helped develop AA4MG + AAXLU :)

You’re very welcome! ^^

Afaik no alternatives yet,
but I can offer some de-googling friendly additions which I developed/contributed to :)

https://github.com/Rikj000/Android-Auto-XLauncher-Unlocked
^ Allows to use 3th party apps on Android Auto

https://github.com/sn-00-x/aa4mg
^ Allows to use Android Auto with MicroG (open source implementation of the GApps)

Khajiit has wares if you have coin.

Sign-up still requires a phone number… -.-"

Checkout Matrix/Element or Session,
there you can actually enjoy privacy by signing-up without a phone number/email:

• https://matrix.org/
• https://element.io/
• ~~https://getsession.org/~~

Edit: Due to Session’s company residing in Australia,
which appareantly has bad privacy laws,
i don’t feel comfortable with recommending it anymore