This program looks interesting
If you also want to learn more about forks, I recommend reading my blog post here:
http://chesstrainerapp.blogspot.fr/2014/01/the-fork.html
You will get some free puzzles and understand how the fork works
Forks Trainer!
Sort:
http://cft.muttsoft.com/
Here's a great app for practicing forks and skewers! helps a lot in improving your tactical vision by using Concentric Square Chess Vision Drill in Michael de la Maza's book Rapid Chess Improvement.
Enjoy :)