"Wiki is the ultimate collaborative WebLog" - this is wrong but very close to right. A Wiki is logically organized (if organized is the right term) and largely timeless. A WebLog is organized by time and (often) a small number of categories. Sometimes time is an important part of recorded thoughts, and other times not. Somehow it seems that wikis and weblogs should not be distinct.
WebLogs tend to be less free-wheeling and more structured than Wiki. Funny - I would have said the opposite.
There are several WebLog applications out there:
RobotWisdomWeblog claims to be the first weblog.