A good description of a WebLog can be found here: http://www.camworld.com/journal/rants/99/01/26.html
"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.
A combination of a Wiki and a WebLog is known by some as a BloggedWiki or a Bliki.
There are several WebLog applications out there:
A feature rich, easy to use blogging platform. Supports multiple DBs like MySQL, PostGres? and also Flat files. http://boastology.com