Open PLAN File
The PLAN file extension and format is a project plan created by Calligra Plan, a project management program included in Calligra Suite.
Calligra Suite is a KDE graphics and office suite.
This software is available for desktop computers, tablets, and smartphones, and contains applications for word processing, spreadsheets, presentations, vector graphics, and database editing.
Its user interface is optimized for use with the keyboard and minimizes the use of dialogues.
The PLAN format stores a list of tasks, resources, and a calendar, as well as the completion level of tasks, which is used to store information for moderately large projects with multiple resources.
Regarding compatibility, the PLAN format was created for use on Linux and does not support other operating systems.
Although it does have the ability to import files from other popular project planning programs, such as Microsoft Project.
Software to open a PLAN file
As stated above, PLAN files can only be run with compatible software on Linux, such as Calligra and Chief Architec.