Feber is a simple and free, self-hostable group calendar application. It is a single PHP file with assets that can run on almost any web host. Feber is database-free and file-based, making it easy to set up, backup, and transfer.

Feber's key features include:

• Event booking and easy repetition of events.

• Four user permission levels ranging from read-only to admin.

• Anonymous viewing/editing link option.

• ICS/ICAL subscription link option.

• Automatic dark/light theme.

• Customizable calendar title and Monday/Sunday week start.

• Localization - currently available in Danish, English, French, German, and Turkish.

Feber focuses on a limited set of features, aiming for simplicity and ease of use. For example, it does not offer CalDAV, multiple calendars per installation, native multi-day booking, or away times. You can install Feber by uploading its files to a directory on your web host and completing the setup form. Backups are created by downloading all files from the directory. Feber can be updated by dragging newer version files onto the existing directory.

A potential issue is that some web hosts have aggressive caching that may prevent PHP scripts from executing. If this happens, you may need to disable or adjust the caching settings or contact your web host's support.