There is clearly much overlap between this category and the main Theravada category. Please submit sites here only if they are very specifically about vipassana. More general Theravadan sites should be submitted there.
Vipassana meditation is a technique originating in the Theravadan Buddhist tradition. One first establishes concentration on a primary object (usually the breath) but then one simply observes the flow of experience in the present moment, with as little strategising and judging as possible. This is described as the practice of "choiceless awareness."