QB64 is a free download at www.qb64.org
QB64 Wiki & Manual is found at www.qb64.org/wiki/Main_Page
QBasic 1.1 is found within OldDOS.exe.
OldDos is a free download at download.microsoft.com/download/win95upg/tool_s/1.0/W95/EN-US/olddos.exe
On some web browsers, the Microsoft link does not work, because the download comes as an exe file.
A zip file of OldDOS can be found at www.pcxt-micro.com/download.html
QBasic 1.1 needs DOSBox to run on Windows Vista and greater, Mac, and Linux.
DosBox is a free download at www.dosbox.com
Free QB64/QBasic Code
QBasic.Net - www.qbasic.net
Pete's QBasic Site - www.petesqbsite.com/index.php
QB45 - qb45.org
Phatcode - games.phatcode.net