Windows 1.01 was the first publicly released retail version of Windows. Windows 1.01 was released on 1985-11-20 and discontinued on 2001-12-31. According to Microsoft, Windows 1.01 is an "Operating Environment" designed to run on top of MS-DOS, rather than a standalone operating system. Additional applications were bundled with Windows, including Write (a word processor), Paint (a graphics drawing program), Reversi (a game), and various utilities (Clock, Calendar, Calculator).
Windows 1.01 initially retailed for $99 in the US or the equivalent of $224.32 in 2017 (accounting for inflation). Windows 1.01 is designed to run on MS-DOS 2.00 to 5.00. If it is loaded on any version of MS-DOS higher than 5.00 (without using setver on win100.bin), it will crash on startup.