A file with .mar extension is a spreadsheet file, created with Mariner Calc application for Mac OSX. It is used to organize data in rows and columns, similar to other spreadsheet file formats such as .xls and .xlsx, and also provides different functions (including Mathematical, Trigonometric, Financial, Date and Time, Logical, Worksheet, Statistical, and Text calculations) to be performed on the data. Mariner Calc supports operations on the spreadsheet data such as creating charts, creating named ranges, data sorting, auto-summation on range, and exporting to .pdf file format for sharing with others.
MAR File Format - More Information
MAR files are saved as binary files in a proprietary file format that is only known to Mariner Calc. Its file format specifications are, therefore, not publicly available to users for writing application to open these files. For this reason, MAR files can only be opened with Mariner Calc application only as of now.