Windows 3.x Calendar
From Just Solve the File Format Problem
Included in Microsoft Windows 3.x, the Calendar software has features which could be saved to a .CAL format.
File Information
The file signature equals the uppercase string CALENDAR encrypted by adding the ASCII values of each letter to the letters in the lowercase string radnelac (calendar spelled backwards). This rather odd encryption technique produces the byte sequence B5 A2 B0 B3 B3 B0 A2 B5.[1][2]
