Microsoft QuickBASIC

A BASIC compiler, interpreter and IDE

QuickBASIC is a twenty year old interpreter/compiler upon which FreeBASIC 
is modeled. It runs in 16-bit MS-DOS.

More information from Wikipedia:

Microsoft QuickBASIC (often shortened, correctly, to QB, or incorrectly, to 
"QBasic", which is a different system) is a descendant of the BASIC 
programming language that was developed by the Microsoft Corporation for 
use with the MS-DOS Operating System.  It was loosely based on GW-BASIC but 
in addition provided user-defined types, improved programming structures, 
better graphics and disk support and a compiler in addition to the 
interpreter. Microsoft sold QuickBASIC as a commercial development suite.

Microsoft released the first version of QuickBASIC on August 18, 1985 
stored on a single 5.25" floppy disk.  QuickBASIC came with a markedly 
different Integrated Design Environment (IDE) from the one supplied with 
previous versions of BASIC.  Line numbers were no longer needed since users 
could insert and remove lines directly via an onscreen text editor. 

Microsoft's "PC BASIC Compiler" was included which could be used to compile 
programs into DOS executables. The editor also had an interpreter built in 
which would run the program without leaving the editor at all, and could be 
used to debug the program before creating an executable file. Unfortunately 
there were some small, subtle differences between the interpreter and the 
compiler, so that sometimes programs running perfectly well in the 
interpreter would fail after compilation, or even not compile at all.

The last version of QuickBASIC was 4.5 (1988) although there was continued 
development of the Microsoft Basic Professional Development System (PDS), 
the last release of which was version 7.1 (June 1990). The PDS version of 
the IDE was called QuickBASIC Extended (QBX). The successor to QuickBASIC 
and PDS was Visual Basic for MSDOS 1.0 provided in Standard and 
Professional versions.  Later versions of Visual Basic did not include DOS 
versions as Microsoft wanted developers to concentrate on Windows 
applications.

A replacement for GW-BASIC, based on QuickBASIC 4.5 was included with 
MS-DOS 5 and later versions.  This is called QBASIC. Compared to QuickBASIC,
it is limited as it lacks a few functions, can only handle programs of a 
limited size, lacks support for separate modules, and is an interpreter 
only. It cannot be used to produce executable files directly although 
programs developed using it can still be compiled by a QuickBASIC 4.5, PDS 
7.1 or VBDOS 1.0 compiler, if one is available.

To learn more about the language, history, and community of QuickBASIC and 
its free interpreter-only counterpart, you should see also 
en.wikipedia.org/wiki/QBasic. There are more links, and more information, 
including a barebones tutorial for Quick/QBasic programming.

External links
    Pete's QB Site. One of the oldest remaining QB sites (since Oct 1998).
    QQN/QBN: QBasic/QuickBasic News.
    QQN's Newbies Section which includes a link for downloading QBasic.