reinvent the wheel
To design or implement a tool equivalent to an existing one or part of one, with the implication that doing so is silly or a waste of time. This is often a valid criticism. On the other hand, automobiles don't use wooden rollers, and some kinds of wheel have to be reinvented many times before you get them right. On the third hand, people reinventing the wheel do tend to come up with the moral equivalent of a trapezoid with an offset axle.