Wearable and Cast are often missed APIs. Contacts and Calendar sync is also not implemented yet. I can't think of any app that I personally used that doesn't work. That includes Google Maps and the Play Store. There were some crashes in the past, but microG became a lot more stable since then.
However, I completely rely on my own infrastructure for mail and contacts / calendar sync (using DAVdroid).
Wearable and Cast are often missed APIs. Contacts and Calendar sync is also not implemented yet. I can't think of any app that I personally used that doesn't work. That includes Google Maps and the Play Store. There were some crashes in the past, but microG became a lot more stable since then. However, I completely rely on my own infrastructure for mail and contacts / calendar sync (using DAVdroid).