It was actually part of Microsoft Plus! for Windows 95. It wasn't directly available for Windows 98 at all, but the Windows 98 install disc does include an INF file so you can install it, provided you have a copy of Plus! for Windows 95.

It was also included with Windows NT 4.0, Windows 2000, Windows Me, and Windows XP (both the original and x64 versions). Finally removed in Vista to never return.