Resource with chess problems in electronic format with solutions I am looking for a database of chess problems in electronic format with solutions. Ideal variant will be a database with something like: 


FEN starting position *
description (Mate in 3 moves, Win material, Black to draw)
solution *
strength of the problem


Only * are really needed, other things just nice to have. It does not matter whether the resource is free or paid. Of course I can get some books and extract such positions by myself, but I hope that someone already have done something like this.
If you are looking for tactical puzzles, there is always CT-Art from Convecta. You can also try Tactic Trainer for Android. It has a nifty difficulty rating system.

Also there is an online resource I forgot to add : http://www.yacpdb.org/