IBM Notes was designed as a collaborative application platform where email was just one of numerous applications that ran in the Notes client software. The Notes client was also designed to run on multiple platforms including Windows, OS/2, classic Mac OS, SCO Open Desktop UNIX, and Linux. These two factors have resulted in the user interface containing some differences from applications that only run on Windows. Furthermore, these differences have often remained in the product to retain backward compatibility with earlier releases, instead of conforming to updated Windows UI standards. The following are some of these differences.