All of them are written by the author of the http://enjoytesting.blogspot.in blog, Ajay Balamurugadas.
He trained with James Bach and is an adept of the context-driven testing school.
These are the links to the books.
They are not free but very cheap ($8 for all 3):
What If - 50 tips for winning testing contests
What If - 50 tips to boost your productivity