Marco Grandis 
CATEGORY THEORY AND APPLICATIONS: A TEXTBOOK FOR BEGINNERS [EPUB ebook] 
A Textbook for Beginners

‘It is written in a pedagogical, at times discursive, style and is both mathematically rigorous and easy to read … The book has an extensive index and can serve as a reference for key definitions and concepts in the subject. It will serve as an easy text for an introductory course in category theory and prove particularly valuable for the student or researcher wishing to delve further into algebraic topology and homological algebra.’
Mathematical Reviews Clippings