Ncurses is a part of the GNU Project. It is one of the few GNU files not distributed under the GNU GPL or LGPL; it is distributed under a permissive free software licence, similar to the MIT License.[8] This is due to the agreement made with the Free Software Foundation at the time the developers assigned their copyright.
When the agreement was made to pass on the rights to the FSF, there was a clause that stated:
The Foundation promises that all distribution of the Package, or of any work
"based on the Package", that takes place under the control of the Foundation
or its agents or assignees, shall be on terms that explicitly and
perpetually permit anyone possessing a copy of the work to which the terms
apply, and possessing accurate notice of these terms, to redistribute copies
of the work to anyone on the same terms.
According to the maintainer Thomas E. Dickey, this precludes relicensing to the GPL in any version, since it would place restrictions on the programs that will be able to link to the libraries.
When the agreement was made to pass on the rights to the FSF, there was a clause that stated:
According to the maintainer Thomas E. Dickey, this precludes relicensing to the GPL in any version, since it would place restrictions on the programs that will be able to link to the libraries.https://en.wikipedia.org/wiki/Ncurses#License