The Libtiff source code repository is now on Gitlab. The old CVS repository on maptools.org will be maintained for historical purposes but won’t get any updates.
One reason for choosing Gitlab rather than Github is that there’s already a libtiff repository on Github. The reasons it’s there aren’t clear, but it’s definitely not an official Libtiff repository.
The Libtiff homepage continues to be on maptools.org.
Mad File Format Science 