A file with .xlr extension is a Microsoft Works Spreadsheet file format that stored data in rows and columns. Microsoft Works was developed for use as an initial productivity suite and remained functional from 1987 to 2009. It included a word processor, a spreadsheet, and a database management system. It was later discontinued after the Microsoft Office was introduced with more rich features included.
XLR File Format - More Informaiton
XLR files were saved as binary files with no details about its file format specifications available publicly. Developers, therefore, do not have an option to analyze its file structure and write applications for reading/writing to these files programmatically. The Works Spreadsheet uses the same Excel file format to store data to .xlr files.