If you are that kind of geek that likes to install a lot of operating systems to toy around and learn new things, than for sure you got bored of installing OSes again and again and again.
In this article I will give you some download links for operating systems and open source software already installed on VirtualBox and VMWare machines, for you just to play.
Virtual images of Linux systems: http://virtualboxes.org/images/
The site provides VirtualBox images of the most popular Linux and *BSD operating systems: Ubuntu, Linux Mint, Fedora, FreeBSD, MINIX,Damn Small Linux, Android X86, et cetera
VMWare images from the VMWare site: https://solutionexchange.vmware.com/store/category_groups/19
This provides a lot of basic installations of Linux systems and many more, and its updated often.
VMWare images for both new and old operating systems: http://www.thoughtpolice.co.uk/vmware/
You can find here, for example, all the Fedora versions from 4 to 18.
This site provides a lot of open source software virtual machines for VMWare: http://www.turnkeylinux.org/
Examples: Drupal 7, CouchDB, Joomla 2.5
This site provides a lot of Open Source VMWare virtual machies: http://bitnami.com/
You have to register in order to download VMs from bitnami, but don’t worry, it’s free.
VMWare images for the most popular new Linux Distributions, like Fedora 18, Ubuntu 13.04, Lubuntu 13.04, Debian 7 and many more can be found here: http://www.traffictool.net/vmware/