Ask HN: Open-source mobile apps worth checking out

I work for a mobile consulting firm and while doing many heterogeneous and diverse projects feels like we get to learn and touch many different concepts and technologies, I also get the feeling that some of the architectural principles and foundations behind our apps are somehow to be considered. We might be doing something wrong project after project.

In order to learn more about what the rest of the industry is doing, I was thinking about organizing meetups to check interesting Open Source projects - e.g. kickstarter engineering team made public their apps some time ago and posted in HN: https://kickstarter.engineering/open-sourcing-our-android-and-ios-apps-6891be909fcd

Do you guys have any suggestions on Open-Source Native or Hybrid apps worth checking?