There is a great program TreeSheets http://strlen.com/treesheets/
It is using a file format .cts that can be opened only with TreeSheets program. This might be sometimes not possible but LibreOffice is much more available.
Steps to Reproduce:
1. Create a file with TreeSheets
2. Open LibreOffice
3. Try to open previously created .cts with LibreOffice
LibreOffice does open the .cts file format and only bunch of garbage symbols are seen.
LibreOffice does open the .cts file format without any issues.
User Profile Reset: No
The TreeSheets program is an open-source - this .cts file format support should be therefore possible to add - https://github.com/aardappel/treesheets/
Thanks for sharing your request. → NEW/enhancement