21 Solitaire Card Games is a free iPhone app developed by A Trillion Games Ltd. It offers a collection of popular solitaire games, including Klondike, FreeCell, Spider, and many more. With its wide variety of solitaire options, this app is sure to keep players entertained for hours.

The app features single-click auto-move functions, making it easy to play the games with just a tap. It also includes an auto-finish feature, allowing players to quickly complete a game if they're stuck. Additionally, the adjustable difficulty level caters to players of all skill levels, from beginners to experts.

One of the standout features of 21 Solitaire Card Games is its hint system, which provides helpful suggestions when players are unsure of their next move. The app also offers a thousand undo/redo levels, allowing players to easily backtrack and try different strategies.

For those who like to keep track of their progress, the app provides persistent/resettable statistics for each solitaire game. This feature allows players to monitor their performance and strive for improvement.

Overall, 21 Solitaire Card Games is a fantastic collection of solitaire games for iPhone users. With its range of game options, adjustable difficulty level, and helpful features, it's a must-have app for solitaire enthusiasts.