Frequently Asked Question List for TeX
There are many commercial implementations of TeX. The first appeared not long after TeX itself appeared.
What follows is probably an incomplete list. Naturally, no warranty or fitness for purpose is implied by the inclusion of any vendor in this list. The source of the information is given to provide some clues to its currency.
In general, a commercial implementation will come “complete”, that is, with suitable previewers and printer drivers. They normally also have extensive documentation (i.e., not just the TeXbook!) and some sort of support service. In some cases this is a toll free number (probably applicable only within the USA and or Canada), but others also have email, and normal telephone and fax support.
PC; TrueTeX Runs on all versions of Windows.
  Richard J. Kinch
  TrueTeX Software
  7890 Pebble Beach Court
  Lake Worth FL 33467
  USA
Tel: +1 561-966-8400
  Email: kinch@truetex.com
  Web: http://www.truetex.com/
  Source: Mail from Richard Kinch, August 2004.
pcTeX Long-established: pcTeX32 is a Windows implementation.
  Personal TeX Inc
  725 Greenwich Street, Suite 210 
  San Francisco, CA 94133
  USA
Tel: 800-808-7906 (within the USA)
  Tel: +1 415-296-7550
  Fax: +1 415-296-7501
  Email: sales@pctex.com
  Web: https://pctex.com/
  Source: Personal TeX Inc web site, December 2004
PC; Scientific Word Scientific Word and Scientific Workplace
offer a mechanism for near-WYSIWYG input of LaTeX documents; they
ship with TrueTeX from Kinch (see above).  Queries within the UK
and Ireland should be addressed to Scientific Word Ltd., others should be
addressed directly to the publisher, MacKichan Software Inc.
  Dr Christopher Mabb
  Scientific Word Ltd.
  130B Main Street
  Yaxley
  Peterborough
  PE7 3LB
  UK
Tel: 0345 766 0340 (within the UK) 
  Fax: 0345 603 9443 (within the UK)
  Email: christopher@sciword.co.uk 
  Web: https://www.sciword.co.uk
MacKichan Software Inc.
  19307 8th Avenue, Suite C
  Poulsbo WA 98370-7370
  USA
Tel: +1 360 394 6033
  Tel: 877 724 9673 (within the USA)
  Fax: +1  360 394 6039
  Email: info@mackichan.com
  Web: http://www.mackichan.com
  Source: Mail from Christopher Mabb, August 2007
AmigaTeX A full implementation for the Commodore Amiga,
including full, on-screen and printing support for all PostScript
graphics and fonts, IFF raster graphics, automatic font generation,
and all of the standard macros and utilities.
  Radical Eye Software
  PO Box 2081
  Stanford, CA 94309
  USA
  Source: Mail from Tom Rokicki, November 1994
Note that the company Y&Y has gone out of business, and Y&Y TeX (and support for it) is therefore no longer available. Users of Y&Y systems may care to use the self-help mailing list that was established in 2003; the remaining usable content of Y&Y’s web site is available at https://www.tug.org/yandy/
FAQ ID: Q-commercial