Extension Manager

Admin Controls Various things to make admins' lives easier
Alias Editor Edit the alias list
BBCode Turns BBCode into HTML
Board Config Allows the site admin to configure the board to his or her taste
Bulk Add Bulk add server-side images
Cron Uploader Uploads images automatically using Cron Jobs
Danbooru Client API Allow Danbooru apps like Danbooru Uploader for Firefox to communicate with Shimmie
Database Upgrader Keeps things happy behind the scenes
Extension Manager A thing for point & click extension management
Favorites Allow users to favorite images
Generic Blocks Add HTML to some space (News, Ads, etc)
Handle MP3 Handle MP3 files
Handle Pixel Handle JPEG, PNG, GIF, etc files
Handle Video Handle FLV, MP4, OGV and WEBM video files.
Home Page Displays a front page with logo, search box and image count
Image Comments Allow users to make comments on images
Image Hash Ban Ban images based on their hash
Image List Show a list of uploaded images
Image Ratings Allow users to rate images "safe", "questionable", "explicit", or "private"
Image Scores (Numeric) Allow users to score images
Image View Counter Tracks & displays how many times an image is viewed
Image Viewer Allows users to see uploaded images
Mail System Provides an interface for sending and receiving mail.
Mass Tagger Tag a bunch of images at once
Metadata Allow admin to store and display various fields of metadata for an image.
Pools System Allow users to create groups of images and order them.
Post Relationships Allow posts to have relationships (parent/child).
RSS for Comments Self explanatory
RSS for Images Self explanatory
Regen Thumb Regenerate a thumbnail image
Rotate Image Allows admins to rotate images.
Simple Wiki A simple wiki, for those who don't want the hugeness of mediawiki
Tag Editor Allow images to have tags assigned to them
Tag History Keep a record of tag changes, and allows you to revert changes.
Tag List Show the tags in various ways
Uploader Allows people to upload files to the website
User Management Allows people to sign up to the website