Fourmilab's Bending Spacetime in the Basement explains how a simple torsion balance can reveal the gravitational attraction between ordinary objects using the same basic principle behind Cavendish's classic experiment.
In 2006, The $39 Experiment mailed 100 handwritten-style requests to 100 companies, tracked the responses publicly, and turned a roll of stamps into a strange little study of corporate generosity.
Project GREAT 2005 turned gravitational time dilation into a family road experiment by taking cesium atomic clocks roughly 4,400 feet higher for about 42 hours and measuring a gain of around 22 nanoseconds.
Stinkymeat2 turned a deliberately disgusting experiment into an 18-day photo diary: six cheap meat products, public locations, daily observations, and exactly the kind of oversharing the early web did best.
Kevin Dunn's old Chemistry 104 site organized chemistry around landmark technologies, asking students to make fire, metals, paper, soap, batteries, glass and other products instead of only reading about them.