Extension Manager

Admin Controls Various things to make admins' lives easier
Alias Editor Edit the alias list
BBCode Turns BBCode into HTML
Browser Search Allows the user to add a browser 'plugin' to search the site with real-time suggestions
Danbooru Client API Allow Danbooru apps like Danbooru Uploader for Firefox to communicate with Shimmie
Favorites Allow users to favorite images
Handle Archives Allow users to upload archives (zip, etc)
Handle Pixel Handle JPEG, PNG, GIF, etc files
Image Comments Allow users to make comments on images
Image List Show a list of uploaded images
Image Ratings Allow users to rate images "safe", "questionable" or "explicit"
Image Scores (Numeric) Allow users to score images
Image Viewer Allows users to see uploaded images
Image Zoom Scales down too-large images using browser based scaling
Link to Image Show various forms of link to each image, for copy & paste
Private Messaging Allow users to send messages to eachother
RSS for Images Self explanatory
Tag Editor Allow images to have tags assigned to them
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