Apps
The base install of the system just contains an email server and Mutt client, but not much else. In addition from within the Administrator control panel under Add/remove apps the following are installable. This list only applies on the home server version, with the mesh network version having a different and smaller set of apps.
DLNA
Enables you to use the system as a music server which any DLNA compatible devices can connect to within your home network.
Dokuwiki
A databaseless wiki system.
Emacs
If you use the Mutt client to read your email then this will set it up to use emacs for composing new mail.
Etherpad
Collaborate on creating documents in real time. Maybe you're planning a holiday with other family members or creating documentation for a Free Software project along with other volunteers. Etherpad is hard to beat for simplicity and speed. Only users of the system will be able to access it.
Ghost
Modern looking blogging system.
GNU Social
Federated social network. You can "remote follow" other users within the GNU Social federation.
Gogs
Lightweight git project hosting system. You can mirror projects from Github, or if Github turns evil then just host your own projects while retaining the familiar fork-and-pull workflow. If you can use Github then you can also use Gogs.
HTMLy
Databaseless blogging system. Quite simple and with a markdown-like format.
Hubzilla
Web publishing platform with social network like features and good privacy controls so that it's possible to specify who can see which content. Includes photo albums, calendar, wiki and file storage.
IRC Server (ngirc)
Run your own IRC chat channel which can be secured with a password and accessible via an onion address. A bouncer is included so that you can receive messages sent while you were offline. Works with Hexchat and other popular clients.
Jitsi Meet
Experimental WebRTC video conferencing system, similar to Google Hangouts. This may not be fully functional, but is hoped to be in the near future.
Lychee
Make your photo albums available on the web.
Mailpile
Modern email client which supports GPG encryption.
Mumble
The popular VoIP and text chat system. Say goodbye to old-fashioned telephony conferences with silly dial codes. Also works well on mobile.
PI-Hole
The black hole for web adverts. Block adverts at the domain name level within your local network. It can significantly reduce bandwidth, speed up page load times and protect your systems from being tracked by spyware.
PostActiv
An alternative federated social networking system compatible with GNU Social. It includes some optimisations and fixes currently not available within the main GNU Social project.
Radicale
Calendar system compatible with CalDAV and CardDAV. Manage your calendar events easily across all your devices.
tt-rss
Private RSS reader. Pulls in RSS/Atom feeds via Tor and is only accessible via an onion address. Have "the right to read" without the Surveillance State knowing what you're reading. Also available with a user interface suitable for viewing on mobile devices via a browser such as OrFox.
Syncthing
Possibly the best way to synchronise files across all of your devices. Once it has been set up it "just works" with no user intervention needed.
Tox
Client and bootstrap node for the Tox chat/VoIP system.
Vim
If you use the Mutt client to read your email then this will set it up to use vim for composing new mail.
XMPP
Chat server which can be used together with client such as Gajim or Conversations to provide end-to-end content security and also onion routed metadata security. Includes advanced features such as client state notification to save battery power on your mobile devices, support for seamless roaming between networks and message carbons so that you can receive the same messages while being simultaneously logged in to your account on more than one device.