I have used many great books, like Levenfish & Smyslov, Emms 'Survival Guide to Rook Endings' (SGRE), Korchnoi 'Practical Rook Endings', Keres 'Practical Chess Endings', de la Villa, Dvoretsky, Nunn's 'Secrets of Rook Endings', etc...
My basic aim is to show the theory on a user friendly environment in simple manner, so that it can be refreshed quickly. If you study nothing else, read de la Villa (incredibly good), but there are many fantastic Endgame books. The iPad version of Forward Chess, excellent too!
I have also collected examples of practical play to put things into perspective.
Constructive criticism or suggestions are very welcome (use the contact me address of the website). 2016: The ‘Basic Section’ of Understanding Rook Endgames, marvellous