If TeX is so good, how come it’s free?
It’s free because Knuth chose to make it so (he makes money from
royalties on his TeX books, which still sell well). He is
nevertheless apparently happy that others should earn money by selling
TeX-based services and products. While several valuable
TeX-related tools and packages are offered subject to restrictions
imposed by the GNU General Public Licence (GPL,
sometimes referred to as ‘Copyleft’), which denies the right to
commercial exploitation. TeX itself is offered under a pretty
permissive licence of Knuth’s own.
There are commercial versions of TeX available; for some users,
it’s reassuring to have paid support. What is more, some of the
commercial implementations
have features that are not available in free versions. (The
reverse is also true: some free implementations have features
not available commercially.)
This FAQ concentrates on ‘free’ distributions of TeX, but we
do at least list the major vendors.
This answer last edited: 2013-06-25
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=whyfree