Wikipedia
WinHelp
Microsoft WinHelp is a proprietary format for online help files that can be displayed by the Microsoft Help browser winhelp.exe or winhlp32.exe. The file format is based on Rich Text Format (RTF). It remained a popular Help platform from Windows 3.0 platform through Windows XP. WinHelp was removed in Windows Vista to discourage software developers from using the obsolete format and encourage use of newer help formats.