Softens jagged edges without blurring the picture. Three different methods, under one control.
msaa takes several samples from slightly different positions within each pixel and averages them, which is what a renderer does natively when you turn on antialiasing. The sample positions sit on a rotated grid, because an axis-aligned one gives poor coverage on the near-horizontal and near-vertical edges that alias worst.
smaa works from the picture rather than from extra samples. It finds the edges, follows each one along to work out how long and how steep it is, and blends across it by an amount that depends on how badly it is stepping. Short, sharply angled runs get the most correction.
blur is the bluntest: an ordinary blur, but applied only where an edge was found, so flat areas stay untouched. strength mixes any of them back against the original.