Answer:
They are alike in the sense that they are websites to communicate and are very interactive.
They are also similar in the fact that anyone can write or edit a wiki about a task or topic of interest, and also anyone can write a blog about a topic of interest and in both cases more people can comment on the page about the theme and encourage dialogue.
Wikis are usually sites with a more academic approach and to expand knowledge while a blog is usually more personal and with more varied topics other than academic stuff.