Everything2
Collaborative encyclopedia from 1999 that took the opposite path to Wikipedia: several personal pieces about the same thing rather than one neutral one.
The site was built by Nate Oostendorp, one of Slashdot's founders, as a successor to the simpler Everything. The structure is nodes — a concept, a word, a title — and under each node sit several independent writeups by different members. One might be a dry definition, the next a personal essay, a third a poem, and all of them stand side by side. An experience-point and level system governed what you were allowed to do, and senior members could promote good pieces. What makes the site interesting in hindsight is that it existed two years before Wikipedia and solved the same problem without requiring anybody to be right.