Freely Available Mathematical Works

Annals of Math
The mathematical journal. Freely available from Project Euclid.
Cornell University's Digital Math Books collection
Handbook of Applied Cryptography
by Alfred J. Menezes, Paul C. van Oorschot and Scott A. Vanstone. Though still in copyright, the authors of this definitive work on cryptography have made the text freely available online.
Journal de Mathématiques Pures et Appliqués
(also known as the "Journal de Liouville"). Full text available from Gallica-math for all but one of the years 1886-1880.
Œuvres compléte.
The complete works of a number of promenent mathematicians, including Abel, Beltrami, Carnot, Cauchy D'Alembert, Dirichlet, Euler, Fourier, Jacobi, Klein, Lagrange, Laguerre, Laplace, Möbius, and Riemann.
Resources at NUMDAM
Michigan University Library's Historical Mathematics Collection

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