From b2evolution manual
This manual page is outdated. NEW PAGE: Plugins/ in b2evolution v5+.
 Plugins Listing
The Akismet plugin for b2evolution checks feedback through a central service against spaminess.
Adds Digg functionality into your b2evolution install.
Adds Last.fm functionality into your b2evolution install.
Allows you to attach Galleries into your posts. Galleries consist of images that you have uploaded, and contain titles and descriptions. You can order images the way you want. Users can view the galleries in multiple display modes.
This Plugin shows a Tag-Cloud using your b2evolution Categories.
The YouTube Plugin allows you to search YouTube, select a video from the results and add it to your post. You don't need to have a YouTube account. You don't need to edit the b2evolution html validator. You don't even need to go to YouTube.com. It's all done from inside your b2evolution backoffice.