There are plenty of "apps" for OwnCloud which are expanding the functional range of the open-source software. Currently at about 110 such addons are available for free download. Some of these addons can be installed directly using the "Apps" menu in the administration interface of OwnCloud - some addons require manual downloading and copying to the apps/ folder on the server using FTP.

My personal selection of useful addons:

EditDoc

EditDoc is a WYSIWYG editor for Owncloud. Using this tool HTML files can be created and modified.

The addon is based on TinyMCE and supports plenty of  formattings and other extra features that makes it look like a WordPad replacement:

• Drag & Drop of pictures (integration using base64)
• Printing function
• Tables
• Links, anchors and breaks

Only drawback: creating new documents is not working for me - files have to be created manually using WebDAV or the official OwnCloud client.

FluXX Compensator (Y)

The FluXX Compensator (Y) is senseful especially for mobile devices.

Using this addon tiny arrows are displayed in the head line and sidebar. When these arrows are selected those bars are hidden or displayed. This makes more space available for the essential content which is senseful especially for mobiles devices because sometimes it is still necessary to access the OwnCloud web interface on the smartphone.

There is an  OwnCloud app for Android but some tasks can be done using this tool - e.g. sharing uploaded files with friends using mails.

But FluXX Compensator (Y) is also useful in combination with the EditDoc addon mentioned above - when the bars are hidden there is more space for the WYSIWYG editor.

Only drawback: it is hard to hit the arrows on smartphones with poor display resolutions.

Checksum

This app extends OwnCloud with MD5 functionality. MD5 checksums of uploaded files can be created comfortably using a mouse click:

Depending on the file size this calculation can take a few seconds to minutes - the checksums are cached for the current folder view. "Hovering" on the file shows up the calculated checksum unless you switch to another folder or view. If the view is switched the checksum has to be re-created - the checksums are not saved.

File move

This tiny but useful addons enables OwnCloud to move or copy files. That's a functionality OwnCloud doesn't provide by default. "Hovering" on the file shows up a "Move" button - by clicking on this button the file can be moved or copied in other folder structures.

Bookmarks (internal app)

Using Bookmarks OwnCloud is able to store bookmarks. Every URL can be described with one or multiple tags so that saved links can be found more quickly.

But there are some functions I miss in this addon - e.g. grouping bookmarks in categories. If you have a big amount of bookmarks you're quickly loosing track.

There is an Android app for using and managing the bookmarks on the way.