Wolfram Research
Wolfram Math World: Leibniz Integral Rule
This page discusses the Leibniz Integral Rule, which concerns "the differentiation of a definite integral whose limits are functions of the differential variable."
Stanford University
Stanford University: Overview of Leibniz
This site outlines Gottfried Wilhelm Leibniz's life. Categories include principal works, Leibniz's life, Leibniz's contributions to philosophy, and further readings.
University of St. Andrews (UK)
University of St. Andrews: Gottfried Wilhelm Von Leibniz
This site from the University of St. Andrews provides a biographical account of the life of Gottfried Wilhelm von Leibniz. Includes links to mathematics topics such as matrices and determinants, quadratic, cubic and quartic equations, etc.