Lotus Notes is a unique environment. It was designed to be a collaborative application platform where email was just one of numerous applications that ran in the Notes client software. Lotus lore has it that the first mail inbox application written by Lotus was a proof-of-concept for a sales presentation. The Notes client was ... designed to run on multiple platforms including Windows, OS/2, Mac, 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 Windows UI standards.