I have a paid version of Shredder for Android that I run on my tablet and really like it. It has many different levels and the cool thing about it for weak players is that at lower levels it makes occasional stupid mistakes such as a poor player might make. Initially I was mystified why a computer chess program would make such a blunder, but it doesn’t do it at higher levels.
In fact, at higher levels it’s really quite good, and certainly unbeatable by me. A few years ago I posted a game between Shredder on my tablet and the famous MacHack program for the PDP-10 mainframe, the first really strong tournament-level chess program. I was able to run MacHack on a PDP-10 simulator on my PC.(that is, the real original MacHack code running on a simulated PDP-10). I ran two games at different MacHack settings, the first at the default level, the second at “tournament” level which was about the highest it could go without running out of memory and crashing. Shredder beat MacHack both times, in 19 and 20 moves, respectively.