This is the result of hours of research, please leave a thanks! and remember that the best way to say thank you to me is to become yourself a fluent speaker of Hindi!
some of these books talk about Hindustani language. It is the old name of Hindi/Urdu when Pakistan, India, Bengal and Nepal was one country. so these books can contain devanagari and persian (urdu) script. but don't worry, the grammar remains the same

LEARN DEVANAGARI SCRIPT

http://www.avashy.com/hindiscripttutor.htm

LEARN HINDI - PDF BOOKS

https://ia600308.us.archive.org/31/i...00hoergoog.pdf
A Grammar of the Eastern Hindi Compared with the Other Gaudian Languages - A. F. Rudolf Hoernle

https://ia700305.us.archive.org/0/it...01kellgoog.pdf
A Grammar of the Hindi Language - Standard Hindi, Braj and Eeastern Hindi of Ramayan of Tulsi Das and the Colloquial Dialects of Marwar Kumaon, Avadh, Baghelkhand, Bhojpur, and more - Rev. S. H. Kellog

https://ia700508.us.archive.org/21/i...00shakrich.pdf
An Introduction to the Hindustani Language, Persian and Devanagari Script - J. Shakespear

https://ia801503.us.archive.org/2/it...hExercises.pdf
Outline of Hindi Grammar with Exercices - Oxford University

https://ia600202.us.archive.org/23/i...00josarich.pdf
Introductory Manual of the Hindi Language - F. P. Luigi Josa

https://ia600303.us.archive.org/0/it...00greauoft.pdf
Hindi Grammar - Edwin Greaves - LONDON MISSIONARY SOCIETY, BENARES

https://ia700306.us.archive.org/6/it...00browgoog.pdf
A Hindi Primer in Roman Character - J. F. Browne

https://ia700400.us.archive.org/7/it...4023098332.pdf
A Grammar of the Hidustani Language in the Oriental and Roman Character - Duncan Forbes

https://ia700502.us.archive.org/4/it...00thimiala.pdf
Hindustani Self Taught with English Phonetic Pronounciation - Captain C. A. Thimm

https://ia600308.us.archive.org/18/i...00thimuoft.pdf
Hindustani Grammar Self Taught in 4 Parts - Captain C. A. Thimm

https://ia600304.us.archive.org/9/it...00kempiala.pdf
The Syntax and Idioms of Hindustani - M. Kempson

https://ia700306.us.archive.org/23/i...00dowsiala.pdf
A Grammar of the Urdu or Hindustani Language - John Dowson

https://ia700508.us.archive.org/5/it...00hoopiala.pdf
The Hindustani Language - W. Hooper

https://ia700508.us.archive.org/23/i...00philuoft.pdf
Hindustani Manual - Lieut. Colonel Phillott

https://ia600401.us.archive.org/11/i...00curtrich.pdf
A Manual of the Hindustani Language as Spoken in Southern India - Lieut. Colonel A. Curtois

https://ia600308.us.archive.org/24/i...00tweerich.pdf
Hidustani as it Ought to be Spoken - J. Tweedie

https://ia700404.us.archive.org/11/i...00pahwuoft.pdf
The Modern Hindustani Scholar or The Pucca Munshi - Munshi Thakardass Pahwa

http://ia700406.us.archive.org/31/it...tudentText.pdf
The Foreign Language Institute, Department of State - An Active Introduction to Hindi -D.N. Sharma & J.W. Stones

http://files.eric.ed.gov/fulltext/ED011654.pdf
The Foreign Language Institute, Department of State - An Active Introduction to Hindi - J.W. Stones & B.G. MacDougall

http://files.eric.ed.gov/fulltext/ED015471.pdf
Glossary to Readings of Hindi Literature - U.S. DEPARTMENT OF HEALTH, EDUCATION & WELFAREOFFICE OF EDUCATION

http://files.eric.ed.gov/fulltext/ED144353.pdf
Lessons in Colloquial Hindustani for Fiji - Smith Sheela

http://hindiurduflagship.org/assets/...Praveshika.pdf
Beginners Hindi Writing and Conversation - H. H. Van Olphen - Hindi Urdu Flagship, The University of Texas at Austin

http://hindiurduflagship.org/assets/...rse-Part_1.pdf
First Year Hindi Course Volume 1 - H. H. Van Olphen - Hindi Urdu Flagship, The University of Texas at Austin

http://hindiurduflagship.org/assets/...1_Workbook.pdf
First Year Hindi Course Volume 1 WORKBOOK - H. H. Van Olphen - Hindi Urdu Flagship, The University of Texas at Austin

http://hindiurduflagship.org/assets/...rse-Part_2.pdf
First Year Hindi Course Volume 2 - H. H. Van Olphen - Hindi Urdu Flagship, The University of Texas at Austin

https://ia700304.us.archive.org/10/i...00smalrich.pdf
A Grammar of the Urdu or Hindustani Language in its Romanized Character - George Small

IMPROVE YOUR KNOWLEDGE ABOUT HINDI - PDF BOOKS

https://ia600407.us.archive.org/15/i...01beamuoft.pdf
Comparative Grammar of the Modern Aryan Languages of India, Hindi, Panjabi, Sindhi, Gujarati, Marathi, Oriya and Bengali Volume 1
John Beames - The University of Calcutta

https://ia600402.us.archive.org/20/i...02beamuoft.pdf
Comparative Grammar of the Modern Aryan Languages of India, Hindi, Panjabi, Sindhi, Gujarati, Marathi, Oriya and Bengali Volume 2
John Beames - The University of Calcutta

https://ia700406.us.archive.org/13/i...03beamuoft.pdf
Comparative Grammar of the Modern Aryan Languages of India, Hindi, Panjabi, Sindhi, Gujarati, Marathi, Oriya and Bengali Volume 3
John Beames - The University of Calcutta

http://hindiurduflagship.org/assets/...since_1800.pdf
Hindi and Urdu Since 1800 - C. Shackle & R. Snell - Study

LEARN HINDI - WEBSITES

http://www.nyu.edu/gsas/dept/mideast/hindi/grammar.html
http://www.learning-hindi.com/intro
http://learn-hindi-online.com/
http://hindilanguage.info/
http://www.ispeakhindi.com/ - OFFLINE (will be fixed soon)
http://www.mindurhindi.com/

update - 5 PDF BOOKS ADDED!

if you know more ressources (especially PDF books), post links below and i will add them to the list. please do not provide many online learning websites as their methods, design, and accuracy are not the best...

update - 1 PDF BOOK ADDED!

A Grammar of the Urdu or Hindustani Language in its Romanized Character - George Small