Richard Lang's legendary post-Mephisto engine Chess Genius is still updating. Although the main code is too old to scale in parallel to hardware improvements, Chess Genius can reach 2500 ELO with a single core on a mobile.
Indeed, one might state it's useless to be interested in such "weak" engine while Stockfish is available. He will be partly right but i'm old enough to appreciate the survival of an old buddy without caring about strength. Memories matter!
I've never owned a Mephisto but i've played with Chess Genius on a Palm Handheld, on a Windows Mobile phone, on IOS, on PC and finally on Android.
The last update from 2.6.4 to 3.0.1 promises some speed up and new time control features making it a great candidate for manual games in Rapidroid. I think i won't keep myself from that if i can find enough spare time (Usually impossible when you have a job!)
For more info on Android version, visit the developer's page: HERE