At three lines, Wikke is probably the edge of the Shortest Wiki Contest. It's a modified version of Jim Ley's JimPUT idea, mentioned previously here on miscoranda, made to conform more to the contest rules using PHP. From the announcement:
Wikke is a 3 line 206 character wiki clone in PHP, JavaScript, and Bash. It was written for the Shortest Wiki Contest by Jim Ley, Sean B. Palmer, and Adam Wendt, with help from Charles Goodier, Arcon, and Daniel Biddle.
The source is small enough now to fit into a sig block. Many thanks to Adam Wendt, aka thelsdj, for the use of his server in developing the code.