Extension Manager

NameDocsDescription

Admin
Show a "down for maintenance" page
Recount / Rename / Etc

Feature
Rough forum extension
Allow users to create groups of images and order them.
Allow users to make comments on images
Show a list of uploaded posts
A simple wiki, for those who don't want the hugeness of mediawiki

File Handling
Bulk add server-side posts with metadata from CSV file
Handle MP3 files
Handle JPEG, PNG, GIF, WEBP, etc files
Handle FLV, MP4, OGV and WEBM video files.
Allows people to replace files for existing posts

General
Edit the alias list
Adds autocomplete to search & tagging.
Turns BBCode into HTML
Renders common elements (thumbnails, paginators) in a way that themes can override
Allow users to favorite images
Allow users to filter out tags.
Add HTML to some space (News, Ads, etc)
Do things with a random post
Blurs thumbs based on rating, users can override. Requires 'Post Ratings'.
Show various bits of system information

Integration
Self explanatory
Self explanatory

Metadata
Allow images to have metadata locked
Annotate images
Allow images to have owners assigned to them
Allow users to rate images "safe", "questionable" or "explicit"
Allow posts to have relationships (parent/child).
Allow users to score images
Allow images to have sources assigned to them
Let tags be split into 'categories', like Danbooru's tagging
Allow images to have tags assigned to them

Moderation
For blocking spam and trolls wiping tags.
Provides query and selection-based bulk action support
Report posts as dupes/illegal/etc
Keep a record of source changes, and allows you to revert changes.
Keep a record of tag changes, and allows you to revert changes.