Some folks have built other software on top of git-annex, or that is designed to interoperate with it.
The git-annex assistant is included in git-annex, and extends its use cases into new territory.
Emacs Org mode can auto-commit attached files to git-annex.
DataLad uses git-annex to provide access to scientific data available from various sources.
The Isuma Media Players project uses git-annex to "create a two-way, distributed content distribution network for communities with poor connexions to the internet".
The Japanese American Legacy Project uses git-annex to manage upwards of 100 terabytes of collections, transporting them from small cultural heritage sites on USB drives. User interface is a Django web app.
gadu - git-annex disk usage is a du like utility that is git-annex aware.
sizes is another du-like utility, with a
-Aswitch that enables git-annex support.
git-annex-watcher is a status icon for your desktop.
See also not for software that is not related to git-annex, but similar.