Where can I find a list of available OS X "Extensions"? OS X Yosemite introduced Extensions, which are listed in the Extensions panel in System Preferences. Currently, the list of "Actions" extensions on my OS X system contains only one item, "Markup".

How can I find more applications and utilities that can be installed as extensions? Is there a categorical list of extensions somewhere?

I tried searching the Mac App Store as well as Googling in general, but "extensions" is such a general term that it produces far too many unrelated results and makes it difficult to find true system extensions. Ideally, I'd like to find a list specifically about proper extensions (if such a list exists), or a better way to search for them (if there is one).
You can search the Mac App Store for apps supporting a specific extension type. For example, searching for appex:com.apple.share-services will show apps that support the share extension. Not all macOS apps are distributed through the Mac App Store, so this isn't an exhaustive list.

Common Mac Extension Types are listed below:


Action: com.apple.ui-services
Audio Unit: com.apple.AudioUnit-UI
Content Blocker: com.apple.Safari.content-blocker
Document Provider: com.apple.fileprovider-ui
Finder Sync: com.apple.FinderSync
Photo Editing: com.apple.photo-editing
Share: com.apple.share-services
Today: com.apple.widget-extension