Rival Chess is an ancient app developed for other platforms before Android. The developer of the Android version is NetAdapt. After a long lasting hiatus, they recently updated it with many new features. I guess the new Rival deserves now to become a serious rival.
Version 2 : *** Major update ***
* 24 Engine levels now (including easier starter levels),
* Save games, and share PGNs,
* UI modernisation,
* Improved sound effects,
* Swipe games to delete them.
Rival Chess can be downloaded from GOOGLE PLAY.