concrete5 does come with a built in blog.
It'd be cool to show how you could set up different groups to be able to post to different areas of a mutli-author blog site:

1) Turn on advanced permissions.
2) Make a few different blog categories.
3) Make a few different groups that will map to those
3.5) Make a general "contributor" group as well.
4) Add some users
5) Setup permissions so users in each group + contributor can post to their various sections.
6) Get all the various corners and task permissions required to pull this off.
7) Eat a cookie or do a victory dance, you're an effn hero.