In this list we have collected all useful and important calculus textbooks in pdf. They are free to download and use.

Elementary Calculus : An approach using infinitesimals by H. J. Keisler

Multivariable Calculus by Jim Herod and George Cain

Calculus by Gilbert Strang for MIT OPEN COURSE WARE

Another Calculus Bible by Neveln

Lecture Notes for Applied Calculus [pdf] by Karl Heinz Dovermann

A Summary of Calculus [pdf] by Karl Heinz Dovermann

First Year Calculus Notes by Paul Garrett

The Calculus of Functions of Several Variables by Professor Dan Sloughter

Difference Equations to Differential Equations : An Introduction to Calculus by Professor Dan Sloughter

Visual Calculus by Lawrence S. Husch

A Problem Text in Advanced Calculus by John Erdman

Understanding Calculus by Faraz Hussain

Advanced Calculus [pdf] by Lynn Loomio and Schlomo Sternberg

The Calculus Wikibook [pdf] on Wiki Media

Vector Calculus

The Calculus for Engineers by John Perry

Calculus Unlimited by J E Marsden & A Weinstein

Advanced Calculus by E B Wilson

Differential and Integral Calculus by Daniel A Murray

Elements of the Differential and Integral Calculus[pdf] by W A Granville & P F Smith

Calculus by Raja Almukkahal, Victor Cifarelli, Chun Tuk Fan & L Jarvis

A course of Pure Mathematics by G. H. Hardy