This is an interesting, somewhat in-depth, ebook on how to create and use a trading system. This does not actually provide you with a trading system but it explains how you can set one up.
This material is geared to a seasoned trader looking to test trading systems and needing some more tools to figure out what it takes to create a successful trading system.
As a forex trader, my concern with these trading systems is that the market is so huge that any trading system almost needs Artificial Intelligence to be of any use.
Nevertheless, this book is worth it if you want to know more about trading systems. Definitely recommend it.