There is only one file type that uses the .TIMELINE extension:
Timeline Data File
A TIMELINE file is a data file created by Timeline, a free, cross-platform program used to create and organize events along a chronological timeline. It contains one or more events and milestones, along with properties, such as the date, description, category, and icon. TIMELINE files are saved in XML format.
TIMELINE files are most often opened by Timeline but they may also be uploaded to and opened by Timeline Viewer in a web browser. Since TIMELINE files are stored in XML format, they may be opened and edited using an XML or text editor.
To create a TIMELINE file in Timeline, select, add events, then select .
To open a TIMELINE file in Timeline, selector and choose the TIMELINE file you want to open.
To export a TIMELINE file in Timeline, selectand choose the format you want to export to, such as .SVG, .CSV, or .PNG.
NOTE: Timeline is open source software and is developed by The Timeline Authors.
Updated: February 3, 2018