A (flawed) rediscovery in 1994 of the trapezoidal rule (Tai, M. M.: A Mathematical Model for the Determination of Total Area Under Glucose Tolerance and Other Metabolic Curves 152–154), a technique for approximating integrals, already discovered as part of Newton's and Leibniz's work on calculus.
Frequently cited as a joke and often referred to as an example of reinventing the wheel.