Linux is an open source software and anyone can take it and create this own Linux (of distribution of Operating system). It's why you can find a lot of distribution on the market :
- Oracle Enterprise Linux (which is derived from Red Hat)
- Ubuntu 8.04 ( The Linux reference ?)
- Mandriva Spring One 2008 ( The challenger ? )
- Fedora 9 ( The most recent version )
- Open Suse 10.3 ( a Swiss army knife )
The distribution (as other applications) in the stack is above the kernel.
For the version, see the dedicated page: Linux - How to know the version of the distribution (Operating system)