Tools should be as simple as they can possibly be. But no simpler. Tools that adhere to this MinimalistDesign far outlast their competitors.

TracVsFitnesse is a fine example of this philosophy. Trac is a lean, toned, sculptured tool, the very embodiment of an OpenSource TechnologicalChangeVector. FitNesse is a fat old cow, bloated with unnecessary features, mired in proprietary development, and encrusted with poorly formulated hyperbole. It was almost obsolete before it started.
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See also KeepItSimple KeepItSimpleMinimalization KeepItSimpleStupid MakeTheSimplestThingThatCouldPossiblyWork AsSimpleAsPossibleButNoSimpler 
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CategorySimplification