Though similar in style to CDK, it is different, being a script-interpreter which provides a set of curses widgets. Widgets are objects whose appearance and behavior can be customized. There is a much-reduced variation of dialog, called lxdialog, which is used in Linux kernel configuration.
DIALOG was written by Savio Lam <lam836@cs.cuhk.hk> and modified by several people.
Initially, I made fixes and reviewed the code to ensure that problems reported were not related to ncurses. After that, I resumed development, adding new widget types. See the changelog for details.
At the end of 2005, I relicensed dialog as LGPL. It was GPL before, which made it (the dialog library in particular) unusable by developers of non-GPL programs. After several requests, I reviewed the code and found that over the course of development and improvements, I had replaced all of the original program. That made me an "original author" of dialog, and allowed me to relicense it.
You should report bugs either to me. or to the ncurses mailing list bug-ncurses@gnu.org.