From there (also from Wiki), I learned that
- Linux is just a kernel while Unix is a complete operating system.
- Unix was originally developed by Dennis Ritchie (also the creator of the C programming language) and Ken Thompson from Bell lab around 1970s, while the Linux kernel was written by a Finnish CS student Linus Torvalds in 1991.
- A typical Linux distribution (or GNU/Linux as Free Software Foundation calls) comprises a Linux kernel, GNU tools and libraries, additional software, documentation, a window system, window manager, and a desktop environment.
- There are 600+ Linux distributions (or GNU/Linux), with 300+ are in active development.
- Some popular mainstream Linux distributions include Debian, Ubuntu, Linux Mint, Fedora, openSUSE, Arch Linux, and the commercial Red Hat Enterprise Linux and SUSE Linux Enterprise Server. Their full relationship/timeline can be referred here: http://upload.wikimedia.org/wikipedia/commons/1/1b/Linux_Distribution_Timeline.svg
- Android is also Linux-based, but does not include a command-line interface and programs made for typical Linux distributions.
- Mac OS is not linux-based. Its version 10, Max OS X is actually a Unix operating system.
- Other popular Unix systems include: HP-UX, IBM AIX, Sun Solairs, IRIX. They are based on different kernels. See details here: http://upload.wikimedia.org/wikipedia/commons/1/1b/Linux_Distribution_Timeline.svg
- iOS is also based on Mac OS X, therefore it's also a Unix OS.