IBM and Compatibles: WINDOWS: MAJORBBS
Additional Notes:
From the excellent themajorbbs.com:

Galacticomm was incorporated in 1985 by Tim Stryker in Fort Lauderdale, Florida, to run a network of multiuser game systems. Stryker had previously designed several game items, including a stand-up arcade game, and a two-player head-to-head game for the Commodore PET called Flash Attack, which was featured in a 1980 Byte magazine article.

In 1984, Stryker wrote a series of multiuser adventure games called Fazuul, Fazuul 9001, Freezuul, and Phazuul. Fazuul ran on a system called EnterNet (the entertainment network).

But the product that started the shift toward BBS software was the Galacticomm Software Breakthrough Library, or, the GSBL. The GSBL was a set of assembler communication routines that programmers could use to write any multiuser application - Galacticomm suggested things like credit-card verification systems, call-forwarding systems, multi-node energy management systems, file transfer systems, multiple listing services, etc. The GSBL provided a multiuser interface to multi-modem cards, multiport serial cards, and COM-port modems. It initially provided support for 32 users under DOS, and was expanded to 64, then 256.
In 1986, Tim Stryker developed the Model 16 multimodem card, which allowed for up to 16 1200-baud modems on one ISA PC card. And, to demonstrate the model 16 and the GSBL, Tim developed The Major BBS v1.0. Later in the year, Galacticomm released partial source code and a non-hardware version of The Major BBS v2.2 as shareware to demonstrate the 'behind the scenes' operation of the system. In 1987, the BBS' version 4.0 was released as a full commercial product. That year, the first ISV products started development.

The Major BBS started catching on; in 1988 version 5.0 shipped along with another innovative hardware product called the Galactibox. The Galactibox was a 16-slot ISA chassis that connected via a cable to an ISA interface card into a PC. Up to four Galactiboxes could be connected to a single PC, allowing 64 less expensive ISA-card internal modems to be connected to the PC. The following year saw the beginning of the explosion of popularity; ANSI support, extended editions to The Major BBS, software connectivity options, and more. More and more ISV products became available.

In 1992, Galacticomm released version 6.0 of the software, which included protected mode support that allowed systems to break the 640K barrier, and use up to 16Mb of memory (much to the relief of operators of very large systems). In 1995, the next major version of the flagship was released, calling itself Worldgroup instead of The Major BBS.

The company was faced with tragedy in August 1996, as founder, Chairman, and chief visionary Tim Stryker passed away. The company was struggling over that past 12 months with sales starting to slow, and trying to position itself favorably with the emerging Internet. Focus was missing, and after Stryker's death, the company was sold in late 1996 by his widow Christine to a group headed by Yannick Tessier, a top ISV. Tessier and Peter Berg led the company toward an IPO, which failed in 1998. By this time, most of the influential members of the company had either left or been let go; the company was bleeding money, and mismanagement forced it to fold in bankruptcy by 2002. The company had essentially shut down operations entirely in 1999. During this whole time, the only major release of the software was Worldgroup 3.0 in February 1997, which was largely completed before the sale to Tessier. Under Tessier, the company released two "point" releases of Worldgroup, and not much else.

A very unfortunate situation for one of the most innovative computer technology companies.

gsblref.pdf ( 30M) DOCUMENTATION: The Galacticommm Software Breakthrough Library Reference, Revision N (January, 1994)
mbbsom.pdf ( 33M) DOCUMENTATION: The MajorBBS Version 6.2 Online Manual by Galacticomm (1994)
entertn.pdf (8.1M) DOCUMENTATION: Entertainment Software Pack by Galacticomm (1992)
mbbstd_1.zip (848K) The MajorBBS Test Drive 6.12 (Part 1)
devguide.pdf ( 35M) DOCUMENTATION: Developer's Guide for the MajorBBS 6.2 by Galacticomm (January, 1994)
majorbbs.zip (118K) The Major BBS by Tim Stryker, GALACTICOMM, Inc. Release 2.2, 24 Jun 86.
mbbstd62.zip (2.1M) The Major BBS Test Drive 6.2 Demo (1993)
faxonln.pdf (3.3M) DOCUMENTATION: Fax/Online from Galacticomm Software (1993)
maillink.pdf (2.2M) DOCUMENTATION: Maillink, by ProStar Software (1993)
richardson.txt (8.0K) An excellent meditation on the experience of MajorBBS, by Steve Richardson (2002)
mbbs4ever.zip (125M) A complete MajorBBS v6.25-256 "Entertainment Edition" BBS w/MajorTCP install for XP/2K/NT
shopmall.pdf (2.9M) DOCUMENTATION: Major BBS Shopping Mall Software (1992)
mbbs4ever.txt ( 12K) README File from mbbs4ever.zip: Listing of Software, Descriptions of Programs
mbbstd_2.zip (1.0M) The MajorBBS Test Drive 6.12 (Part 2)