If I had to type all the Linux distros that exist, I'd be here for a long time.
Common ones are:
Ubuntu (and derivatives such as Kubuntu, Xubuntu, Lubuntu, etc.)
openSUSE
Fedora
Debian
Mint
There are many open-source OS distributions (distros) branching out from the Linux Kernel. Ubuntu, Linux Mint, Puppy, to name but three.
This is a holding question for alternates dealing with long-obsolete Linux distributions, such as Red Hat Linux 9. Please do not split the alternates out. There is no reason to use these distributions; they no longer receive any security updates, may not run on modern hardware, and many modern Linux distributions are free.
There is no such thing as "Linux XP". If you're referring to Windows XP, then the answer is no. As far as Linux distributions, for the majority of distributions, they are free (as in freedom) and free-of-charge.
Most Linux distributions are free
Many Linux distributions are intended for home users.
"Distros", or distributions.
There are many ways to categorize Linux distributions. You can categorize them by their size, whether they run on a LiveCD, whether they are provided gratis, their ancestry of other Linux distros, and the purpose the distro is meant to serve.
Distributions
Nothing. Most Linux distributions are free of charge. There are some distributions that are commercially sold, though those sales are more likely subscriptions for support, not for the Linux distribution itself.
the kernal is the central part of the Linux operating system and determines how the system works - all distributions of Linux are based on this.
The Linux kernel. Beyond that, there are numerous alternative implementations of virtually every Linux program.
Linux is open source, not shareware or proprietary. There are commercial Linux distributions.