From b2evolution manual
This manual page is outdated. NEW PAGE: Multiple Blogs in b2evolution v5+.
One of the strengths of b2evolution is that it is able to handle multiple blogs out of the box. As a matter of fact, on most installations it will come with multiple blogs pre-installed.
 Multiblog Scenarios
Multiple blogs can be used in several different scenarios:
- One website with multiple blogs accessible through different names - blog1.php, blog2.php, blog3.php, etc. This is the default setup, you can then change the names of the php files to suit your needs. Each blog can also have a different subject, purpose or even content type - i.e., podcasts, or photoblogs.
- One website with multiple blogs scattered through a complex tree of subfolders.
- One domain with multiple blogs accessible through subdomains - blog1.domain.com, blog2.domain.com, etc. Again, you can choose any name to suit your needs.
- One b2evolution installation serving multiple domains.
- Any combination of the above.
 Using Multiple Blogs
- Sample blogs : Blog A & B, Linkblog...
- Using stub files to anchor particular blogs in particular locations of your website.
- Using summary.php
- Using multiblogs.php