The other one is DroidFish with the Stockfish engine. DroidFish is one of the strongest free programs available for android devises. Advantages of DroidFish (besides having the Stockfish engine) are the ability to setup a position and to run a computer analysis. It has various playing modes: you can play against a computer, two people, engine vs. engine play and adjustable playing strength. You can also load/save/annotate pgn games, use external opening books and do position analysis. It has a wide variety of colors and themes and it offers book hints. With a comprehensive settings menu and multiple engine support, it's more or less a serious program...not what you want to play against while while sitting around a hotel room, in the airport, etc. as I was last week. For that you want Chess Free because it plays a challenging game and it's strength is probably somewhere under 1800.
At 5 minutes per game, I lost most of the time, but after bumping up the time limit to 10 minutes per game I was able to win most of the games.
The app includes a chess tutor, clocks, 12 playing levels and various features such as game preview and analysis. It is one of the most downloaded chess program on Android.
One thing I like about Chess Free is the 2 meg opening book which gives it a pretty wide variety of opening play and it goes to a decent depth.
It runs on the Treebeard engine by Jeff Rollason and Didzis Cirulis. According to the authors the engine has a complex Swapping Off Material Analyzer (SOMA) of the whole board, considers pins and ties to defend against captures, forks and even mate threats, guided by a probability-based tree search...whatever all that means.
I saved the games and downloaded them to my laptop and here is one of the more interesting games. When things got tactical both sides displayed a lack of tactical ability which is why this engine is probably a good one for those of us who are rating challenged to play against!