The Debian/Ubuntu family was started with support from the Free Software Foundation. They wanted a Linux distribution that represented the community supported free software model. At one point Debian was the only Linux distribution that was really considered free by Richard Stallman the founder of the Free Software movement and author of the GNU General Public License (GPL).
The Debian family of distributions use packages with the .deb file extension. While Debian and Ubuntu two are different distros they are so close that they are often mentioned together, but they are indeed separate distros.
The following are a few well known Debian based Linux distributions:
Debian GNU/Linux - https://www.debian.org/
Linux Mint: a modern, elegant and comfortable operating system which is both powerful and easy to use.
Ubuntu: popularising Linux around the world.Kali Linux: security auditing and penetration testing
Grml: live system for system administrators
- Purism PureOS: FSF-endorsed rolling release, focused on privacy, security and convenience.
- Tails: preserve privacy and anonymity