I now know of three mobile Steem apps.
By Matthew Brady, Public Domain
@steemapp's Steemy is written in native Swift for iOS and Java for Android. @str11ngfello is doing the iOS version. @cyonic is working on Android. They plan to open source the crypto, but not the rest of the app. They tagged their single article so far with #steemy. They've promised a public beta soon. This is the most featurefully promised of the three.
@riensen's Steem app is iOS only. Looks nice. Open source (github.com/riensen/steem-app). Riensen has been helping me to get it to build on my Mac. They say they have a public beta, but my email asking for it went unanswered. No news since the announcement almost three weeks ago. And no GitHub commits.